FYI the latest version didn't fix the Monarch errors.
Same here - Custom 4.2 runs seamlessly, all other versions max out at around 400GH/s spewing errors....
Here is a piece of the 4.9 debug.log.
[2014-10-09 21:00:56] Selecting pool 0 for work
[2014-10-09 21:00:56] Generated stratum header 000000026cc3743b64607497796354162e5960858160187c124efcd90000000000000000dccfa7bf2be99aad34d43ece09c70824d9a761d36dc960a47ce12da9bca0308b54372fd6181f697300000000
[2014-10-09 21:00:56] Work job_id 1412902870 385095 nonce2 24010000
[2014-10-09 21:00:56] Generated stratum work
[2014-10-09 21:00:56] Pushing work 90087 from pool 0 to hash queue
[2014-10-09 21:00:56] Selecting pool 0 for work
[2014-10-09 21:00:56] Generated stratum header 000000026cc3743b64607497796354162e5960858160187c124efcd90000000000000000b5c5806b76a3a87bff6a356b5d2ecf2c3864439da486030b6e0acfcac601bbce54372fd6181f697300000000
[2014-10-09 21:00:56] Work job_id 1412902870 385095 nonce2 25010000
[2014-10-09 21:00:56] DEVPROTO: BFL 1: GETS: INPROCESS:0
[2014-10-09 21:00:56] DEVPROTO: BFL 4: GETS: BIN-InP:056 FLUSHED:057
[2014-10-09 21:00:56] DEVPROTO: BFL 1: GETS: COUNT:9
[2014-10-09 21:00:56] DEVPROTO: BFL 1: GETS: 08D4,3E,1,DDDD20E8
[2014-10-09 21:00:56] BFL 4aa: Sanity check: Device work count mismatch (dev inproc=56, dev flushed=57, queued=256)
[2014-10-09 21:00:56] Generated stratum work
[2014-10-09 21:00:56] DEVPROTO: BFL 1: GETS: 08CA,55,1,17B2F24F
[2014-10-09 21:00:56] DEVPROTO: BFL 4: READ(226): 417941504147414d4171416c4166415741514167414841754163413e416d416e415c4168416f415d4149415e416941524158415f41534154416a4172417b4160414b4161414e4170414241594177414f41554156415a414c4173416441654174416b415b4178410c41404143414a4146393439353936393739383939393a393b393c393d4112417e41044124411d41194109410d411e417a4127411a4176411f4120410e411b41214113417f41144122410a410f41154105410b4123412541104100411141014126417c4116412841064102410741084103412941174118411c417d
[2014-10-09 21:00:56] Pushing work 90089 from pool 0 to hash queue
[2014-10-09 21:00:56] DEVPROTO: BFL 1: GETS: 08C7,33,2,7451A707,B29DDF39
[2014-10-09 21:00:56] BFL 4aa: Sanity check: Device is missing queued job! b934
[2014-10-09 21:00:56] DEVPROTO: BFL 2: GETS: BIN-InP:090 FLUSHED:111
[2014-10-09 21:00:56] DEVPROTO: BFL 1: GETS: 08BD,2E,1,D7F0AA7E
[2014-10-09 21:00:56] BFL 4aa: Sanity check: Device is missing queued job! b935
[2014-10-09 21:00:56] BFL 2aa: Sanity check: Device work count mismatch (dev inproc=90, dev flushed=111, queued=256)
[2014-10-09 21:00:56] DEVPROTO: BFL 1: GETS: 08C9,53,3,1990FAD0,5166067A,98DC8991
[2014-10-09 21:00:56] BFL 4aa: Sanity check: Device is missing queued job! b936
[2014-10-09 21:00:56] DEVPROTO: BFL 2: READ(402): 760b764a7628760e7630764b7603760f762976107615763d763e762a767d76317616765376177674762b7675762c7676763f762d76207611767f760c7618764076557656762e7619767776057641763276127621761376227623761a7633762476347614761b764d7635765876257636764e762f76377638761c76397626765a7608763a7642761d763b765c763c7643761e761f7627760a76447645764f7646760d7647764876497650765f7667760976067607674b674c674d674e674f6750675167526753675467556756675767587668771676787669770977177651766a767d7660766b77187719767e7652770a767f771a7671764c7700765477017659771b7702770b766c766176727679770c771c771d7703770476577662771e770d766377057664767a767b767377067674770776657666771f77087675770e7720674b674c674d674e674f6750675167526753675467556756770f7710771176767712767c765b77137721766d77147723771577227677766e766f765d7724772577267727765e772876707729772a772b772c
[2014-10-09 21:00:56] DEVPROTO: BFL 0: GETS: BIN-InP:067 FLUSHED:120
[2014-10-09 21:00:56] DEVPROTO: BFL 1: GETS: 08B1,1B,0
[2014-10-09 21:00:56] BFL 4aa: Sanity check: Device is missing queued job! b937
[2014-10-09 21:00:56] BFL 2aa: Sanity check: Device is missing queued job! e74b
[2014-10-09 21:00:56] DEVPROTO: BFL 1: GETS: 08C6,29,1,BFEE5086
[2014-10-09 21:00:56] BFL 0aa: Sanity check: Device work count mismatch (dev inproc=67, dev flushed=120, queued=255)
[2014-10-09 21:00:56] BFL 4aa: Sanity check: Device is missing queued job! b938
[2014-10-09 21:00:56] DEVPROTO: BFL 3: GETS: BIN-InP:122 FLUSHED:111
[2014-10-09 21:00:56] BFL 2aa: Sanity check: Device is missing queued job! e74c
[2014-10-09 21:00:56] DEVPROTO: BFL 1: GETS: 08C5,1A,0
[2014-10-09 21:00:56] DEVPROTO: BFL 0: READ(374): 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
[2014-10-09 21:00:56] BFL 4aa: Sanity check: Device is missing queued job! b939
[2014-10-09 21:00:56] BFL 3aa: Sanity check: Device work count mismatch (dev inproc=122, dev flushed=111, queued=249)
[2014-10-09 21:00:56] BFL 2aa: Sanity check: Device is missing queued job! e74d
[2014-10-09 21:00:56] DEVPROTO: BFL 1: GETS: 08D3,3D,1,219215BA
[2014-10-09 21:00:56] BFL 0aa: Sanity check: Device is missing queued job! e383
[2014-10-09 21:00:56] BFL 4aa: Sanity check: Device is missing queued job! b93a
[2014-10-09 21:00:56] DEVPROTO: BFL 3: READ(466): 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
[2014-10-09 21:00:56] BFL 2aa: Sanity check: Device is missing queued job! e74e
[2014-10-09 21:00:56] Selecting pool 0 for work
[2014-10-09 21:00:56] DEVPROTO: BFL 1: GETS: OK
[2014-10-09 21:00:56] BFL 0aa: Sanity check: Device is missing queued job! e385
[2014-10-09 21:00:56] BFL 4aa: Sanity check: Device is missing queued job! b93b
[2014-10-09 21:00:56] BFL 3aa: Queue flush: 421b inprogress
[2014-10-09 21:00:56] BFL 2aa: Sanity check: Device is missing queued job! e74f
[2014-10-09 21:00:56] BFL 0aa: Sanity check: Device is missing queued job! e389
[2014-10-09 21:00:56] BFL 4aa: Sanity check: Device is missing queued job! b93c
[2014-10-09 21:00:56] BFL 3aa: Queue flush: 4231 inprogress
[2014-10-09 21:00:56] BFL 2aa: Sanity check: Device is missing queued job! e750
[2014-10-09 21:00:56] Generated stratum header 000000026cc3743b64607497796354162e5960858160187c124efcd900000000000000008a291784a35dfb2f64ae73f2facb570f007af088320fae81c421645f36ef491054372fd6181f697300000000
[2014-10-09 21:00:56] BFL 1aa: Received 9 queue results on poll (max=16)
[2014-10-09 21:00:56] BFL 0aa: Sanity check: Device is missing queued job! e38a
[2014-10-09 21:00:56] BFL 4aa: Sanity check: Device is missing queued job! b93d
[2014-10-09 21:00:56] BFL 3aa: Queue flush: 4233 inprogress
[2014-10-09 21:00:56] BFL 2aa: Sanity check: Device is missing queued job! e751
[2014-10-09 21:00:56] Work job_id 1412902870 385095 nonce2 26010000
[2014-10-09 21:00:56] BFL 1ck: Queue result: 08D4,3E,1,DDDD20E8
[2014-10-09 21:00:56] BFL 0aa: Sanity check: Device is missing queued job! e38c
[2014-10-09 21:00:56] BFL 4aa: Sanity check: Device is missing queued job! c13e
[2014-10-09 21:00:56] BFL 3aa: Queue flush: 4237 inprogress
[2014-10-09 21:00:56] BFL 2aa: Sanity check: Device is missing queued job! e752
[2014-10-09 21:00:56] Generated stratum work
[2014-10-09 21:00:56] BFL 0aa: Sanity check: Device is missing queued job! e38d
[2014-10-09 21:00:56] BFL 4aa: Sanity check: Device is missing queued job! c140
[2014-10-09 21:00:56] BFL 3aa: Queue flush: 4238 inprogress
[2014-10-09 21:00:56] BFL 2aa: Sanity check: Device is missing queued job! e753
[2014-10-09 21:00:56] Pushing work 90091 from pool 0 to hash queue
[2014-10-09 21:00:56] Proof: 000000007e17dd7d4022cb7a03e6d4d4a474295abfa1875947ac96a620819fe9
Target: 000000000080000000ffffffffffffffffffffffffffffffffffffffffffffff
TrgVal? no (false positive; hash > target)
[2014-10-09 21:00:56] BFL 0aa: Sanity check: Device is missing queued job! e38e
[2014-10-09 21:00:56] BFL 4aa: Sanity check: Device is missing queued job! c142
[2014-10-09 21:00:56] BFL 3aa: Queue flush: 4248 inprogress
[2014-10-09 21:00:56] BFL 2aa: Sanity check: Device is missing queued job! e754
[2014-10-09 21:00:56] BFL 0aa: Sanity check: Device is missing queued job! e38f
[2014-10-09 21:00:56] BFL 4aa: Sanity check: Device is missing queued job! c143
[2014-10-09 21:00:56] BFL 3aa: Queue flush: 424a inprogress
[2014-10-09 21:00:56] BFL 2aa: Sanity check: Device is missing queued job! e755
[2014-10-09 21:00:56] BFL 0aa: Sanity check: Device is missing queued job! e391
[2014-10-09 21:00:56] BFL 4aa: Sanity check: Device is missing queued job! c146
[2014-10-09 21:00:56] BFL 3aa: Queue flush: 424d inprogress
[2014-10-09 21:00:56] BFL 2aa: Sanity check: Device is missing queued job! e756
[2014-10-09 21:00:56] BFL 1dh: Queue result: 08CA,55,1,17B2F24F
[2014-10-09 21:00:56] BFL 0aa: Sanity check: Device is missing queued job! e392
[2014-10-09 21:00:56] BFL 4aa: Sanity check: Device is missing queued job! c147
[2014-10-09 21:00:56] BFL 3aa: Queue flush: 424e inprogress
[2014-10-09 21:00:56] BFL 2aa: Sanity check: Device is missing queued job! e757
[2014-10-09 21:00:56] BFL 0aa: Sanity check: Device is missing queued job! e393
[2014-10-09 21:00:56] BFL 4aa: Sanity check: Device is missing queued job! c148
[2014-10-09 21:00:56] BFL 3aa: Queue flush: 424f inprogress
[2014-10-09 21:00:56] BFL 2aa: Sanity check: Device is missing queued job! e758
[2014-10-09 21:00:56] Proof: 000000001ed2c1dd6df98690aaf31319f97fb670ef204797656c08ed6da03b55
Target: 000000000080000000ffffffffffffffffffffffffffffffffffffffffffffff
TrgVal? no (false positive; hash > target)
[2014-10-09 21:00:56] BFL 0aa: Sanity check: Device is missing queued job! e394
[2014-10-09 21:00:56] BFL 4aa: Sanity check: Device is missing queued job! c149
[2014-10-09 21:00:56] BFL 3aa: Queue flush: 4251 inprogress
[2014-10-09 21:00:56] BFL 2aa: Sanity check: Device is missing queued job! e7cb
[2014-10-09 21:00:56] BFL 0aa: Sanity check: Device is missing queued job! e395
[2014-10-09 21:00:56] BFL 4aa: Sanity check: Device is missing queued job! c14a
[2014-10-09 21:00:56] BFL 3aa: Queue flush: 4252 inprogress
[2014-10-09 21:00:56] BFL 2aa: Sanity check: Device is missing queued job! e7cc
[2014-10-09 21:00:56] Selecting pool 0 for work
[2014-10-09 21:00:56] BFL 0aa: Sanity check: Device is missing queued job! e396
[2014-10-09 21:00:56] BFL 4aa: Sanity check: Device is missing queued job! c14b
[2014-10-09 21:00:56] BFL 3aa: Queue flush: 4253 inprogress
[2014-10-09 21:00:56] BFL 2aa: Sanity check: Device is missing queued job! e7cd
[2014-10-09 21:00:56] BFL 1bz: Queue result: 08C7,33,2,7451A707,B29DDF39
[2014-10-09 21:00:56] BFL 0aa: Sanity check: Device is missing queued job! e397
[2014-10-09 21:00:56] BFL 4aa: Sanity check: Device is missing queued job! c14c
[2014-10-09 21:00:56] BFL 3aa: Queue flush: 4255 inprogress
[2014-10-09 21:00:56] BFL 2aa: Sanity check: Device is missing queued job! e7ce
[2014-10-09 21:00:56] Generated stratum header 000000026cc3743b64607497796354162e5960858160187c124efcd90000000000000000d482d26b3ffb213098991d854d0e41fb32ec53090f3aa7e847cc535a1d65f6e054372fd6181f697300000000
[2014-10-09 21:00:56] BFL 0aa: Sanity check: Device is missing queued job! e398
[2014-10-09 21:00:56] BFL 4aa: Sanity check: Device is missing queued job! c14d
[2014-10-09 21:00:56] BFL 3aa: Queue flush: 4256 inprogress
[2014-10-09 21:00:56] BFL 2aa: Sanity check: Device is missing queued job! e7cf
[2014-10-09 21:00:56] Work job_id 1412902870 385095 nonce2 27010000
[2014-10-09 21:00:56] Proof: 000000000670e383cdeb20df1790011cd668800f693258e6e1fd624bd6764318
Target: 000000000080000000ffffffffffffffffffffffffffffffffffffffffffffff
TrgVal? no (false positive; hash > target)
[2014-10-09 21:00:56] BFL 0aa: Sanity check: Device is missing queued job! e399
[2014-10-09 21:00:56] BFL 4aa: Sanity check: Device is missing queued job! c14e
[2014-10-09 21:00:56] BFL 3aa: Queue flush: 4259 inprogress
[2014-10-09 21:00:56] BFL 2aa: Sanity check: Device is missing queued job! e7d0
[2014-10-09 21:00:56] Generated stratum work
[2014-10-09 21:00:56] BFL 0aa: Sanity check: Device is missing queued job! e39a
[2014-10-09 21:00:56] BFL 4aa: Sanity check: Device is missing queued job! c14f
[2014-10-09 21:00:56] BFL 3aa: Queue flush: 425a inprogress
[2014-10-09 21:00:56] BFL 2aa: Sanity check: Device is missing queued job! e7d1
[2014-10-09 21:00:56] Pushing work 90096 from pool 0 to hash queue
[2014-10-09 21:00:56] BFL 0aa: Sanity check: Device is missing queued job! e39b
[2014-10-09 21:00:56] BFL 4aa: Sanity check: Device is missing queued job! c150
[2014-10-09 21:00:56] BFL 3aa: Queue flush: 425b inprogress
[2014-10-09 21:00:56] BFL 2aa: Sanity check: Device is missing queued job! e7d2
[2014-10-09 21:00:56] BFL 0aa: Sanity check: Device is missing queued job! e39c
[2014-10-09 21:00:56] BFL 4aa: Sanity check: Device is missing queued job! c151
[2014-10-09 21:00:56] BFL 3aa: Queue flush: 425e inprogress
[2014-10-09 21:00:56] BFL 2aa: Sanity check: Device is missing queued job! e7d3
[2014-10-09 21:00:56] Proof: 000000008828189130a13ddfb1bcd64a4ea20401bc80652c9af33bb63750c1d5
Target: 000000000080000000ffffffffffffffffffffffffffffffffffffffffffffff
TrgVal? no (false positive; hash > target)
[2014-10-09 21:00:56] BFL 0aa: Sanity check: Device is missing queued job! e39d
[2014-10-09 21:00:56] BFL 4aa: Sanity check: Device is missing queued job! c152
[2014-10-09 21:00:56] BFL 3aa: Queue flush: 425f inprogress
[2014-10-09 21:00:56] BFL 2aa: Sanity check: Device is missing queued job! e7d4
[2014-10-09 21:00:56] BFL 0aa: Sanity check: Device is missing queued job! e39e
[2014-10-09 21:00:56] BFL 4aa: Sanity check: Device is missing queued job! c153
[2014-10-09 21:00:56] BFL 3aa: Queue flush: 4261 inprogress
[2014-10-09 21:00:56] BFL 2aa: Sanity check: Device is missing queued job! e7d5
[2014-10-09 21:00:56] BFL 0aa: Sanity check: Device is missing queued job! e39f
[2014-10-09 21:00:56] BFL 4aa: Sanity check: Device is missing queued job! c154
[2014-10-09 21:00:56] BFL 3aa: Queue flush: 4262 inprogress
[2014-10-09 21:00:56] BFL 1bu: Queue result: 08BD,2E,1,D7F0AA7E
... on and on and on, eventually ....
[2014-10-09 21:00:57] BFL 2aa: Sanity check: Device is processing unknown work 4a760000 (1)
[2014-10-09 21:00:57] Work job_id 1412902870 385095 nonce2 46010000
[2014-10-09 21:00:57] BFL 3aa: Popping work from get queue to get work
[2014-10-09 21:00:57] BFL 4aa: Appending to driver queue (max=256, ready=3, queued<=77)
[2014-10-09 21:00:57] BFL 2aa: Sanity check: Device is processing unknown work 0b760000 (1)
[2014-10-09 21:00:57] Generated stratum work
[2014-10-09 21:00:57] BFL 4aa: Popping work from get queue to get work
[2014-10-09 21:00:57] BFL 2aa: Flushed 111 jobs from device and 0 from driver (queued<=-56)
[2014-10-09 21:00:57] Pushing work 90165 from pool 0 to hash queue
[2014-10-09 21:00:57] BFL 2aa: Sanity check: Device work inprogress count mismatch (dev inproc=90, queued=-56)
[2014-10-09 21:00:57] BFL 1aa: Got work 90109 from get queue to get work for thread 128
[2014-10-09 21:00:57] BFL 2aa: Popping work from get queue to get work
[2014-10-09 21:00:57] BFL 1aa: Appending to driver queue (max=256, ready=10, queued<=91)
[2014-10-09 21:00:57] BFL 3aa: Got work 90111 from get queue to get work for thread 384
[2014-10-09 21:00:57] BFL 1aa: Popping work from get queue to get work
[2014-10-09 21:00:57] BFL 3aa: Appending to driver queue (max=256, ready=3, queued<=123)
[2014-10-09 21:00:57] BFL 4aa: Got work 90113 from get queue to get work for thread 512
[2014-10-09 21:00:57] BFL 3aa: Popping work from get queue to get work
[2014-10-09 21:00:57] BFL 4aa: Appending to driver queue (max=256, ready=4, queued<=77)
[2014-10-09 21:00:57] BFL 4aa: Popping work from get queue to get work
[2014-10-09 21:00:57] BFL 2aa: Got work 90115 from get queue to get work for thread 256
[2014-10-09 21:00:57] BFL 2aa: Appending to driver queue (max=256, ready=1, queued<=90)
[2014-10-09 21:00:57] BFL 1aa: Got work 90117 from get queue to get work for thread 128
[2014-10-09 21:00:57] Selecting pool 0 for work
[2014-10-09 21:00:57] DEVPROTO: BFL 2aa: CMD1 HEX: 57583400c101c783aaabd15362a97c0febff0155bedcccf47e557899e68c72f5828ca1db0761a2c3a33554372fd6181f6973aafe
[2014-10-09 21:00:57] BFL 1aa: Appending to driver queue (max=256, ready=11, queued<=91)
[2014-10-09 21:00:57] BFL 3aa: Got work 90119 from get queue to get work for thread 384
[2014-10-09 21:00:57] BFL 1aa: Popping work from get queue to get work
[2014-10-09 21:00:57] Generated stratum header 000000026cc3743b64607497796354162e5960858160187c124efcd9000000000000000091b76eb6b925ac980c273f364e5299ceac2d355b163b473c482e7e16df82bf5354372fd6181f697300000000
[2014-10-09 21:00:57] BFL 3aa: Appending to driver queue (max=256, ready=4, queued<=123)
Interesting that it sometimes reports a negative queued number, e.g. (queued<=-56)...