Do you use a Scrypt-Jane miner? If not {look in the OP for one that matches you's OS.}
That is the one!
What's your settings so far?
setx GPU_MAX_ALLOC_PERCENT 100
setx GPU_USE_SYNC_OBJECTS 1
cgminer.exe --scrypt-jane --sj-nfmin 4 --sj-nfmax 30 --sj-time 1388949883 -o stratum+tcp://cach.catcoin.cz:3333 -u LowSkiII.1 -p 123 -I 13 -g 1 -w 256 --lookup-gap 2 --thread-concurrency 8193 --no-submit-stale --expiry 10 --scan-time 1 --queue 0 --temp-cutoff 90
setx GPU_MAX_ALLOC_PERCENT 100
setx GPU_USE_SYNC_OBJECTS 1
cgminer.exe --scrypt-jane --sj-nfmin 4 --sj-nfmax 30 --sj-time 1388949883 -o stratum+tcp://cach.catcoin.cz:3333 -u LowSkiII.1 -p 123
Have 2x 280x.Gigabyte rev.3 and msi gaming both 3 gb.
-I 13 is a bit high i think... arn't you getting spammed with HW errors?
Try lowering it, i can't remember how much but try halving it. No HW err the up 50% and so on...