Someone could be forking the coin with lots of hash.
No. It was hit by the time wrap bug:
$ starcoind getblock 00000001219aabf7a0c0e629bacf6b70cbd857ebeb7e2575c6049c70306b5190
{
"hash" : "00000001219aabf7a0c0e629bacf6b70cbd857ebeb7e2575c6049c70306b5190",
"confirmations" : 1,
"size" : 268,
"height" : 777855,
"version" : 4,
"merkleroot" : "0221710eae6afdcc6cec652e513b74898e9929da0fa14d6124c157565ccd66e9",
"mint" : 100.00000000,
"time" : 1400607967,
"nonce" : 2163618803,
"bits" : "1d03cb20",
"difficulty" : 0.26360777,
"previousblockhash" : "00000000dfa28f824f3c569dbe8ae78c6dd0bb659f084f48d6c72a70277fd76c",
"flags" : "proof-of-work",
"proofhash" : "00000001219aabf7a0c0e629bacf6b70cbd857ebeb7e2575c6049c70306b5190",
"entropybit" : 0,
"modifier" : "dc6c78fb8aaa45f0",
"modifierchecksum" : "56e6bebb",
"tx" : [
"0221710eae6afdcc6cec652e513b74898e9929da0fa14d6124c157565ccd66e9"
],
"signature" : "30460221008f5a3e299781b03df544c442b1461a6724257b327550be38a568505bd01ad06e02210 0a7ab840456c6054aec1f0b7373226d5f8c6c9fd4bd4a25ad4107d7e3b70b587a"
}
$ starcoind getblock 00000000dfa28f824f3c569dbe8ae78c6dd0bb659f084f48d6c72a70277fd76c
{
"hash" : "00000000dfa28f824f3c569dbe8ae78c6dd0bb659f084f48d6c72a70277fd76c",
"confirmations" : 2,
"size" : 268,
"height" : 777854,
"version" : 4,
"merkleroot" : "a7ed902b6a2dee6a5045d277d19b50c77db83d3b4e7ce55cf203ca59a62db8e3",
"mint" : 100.00000000,
"time" : 1400608554,
"nonce" : 3908568320,
"bits" : "1d03fb5b",
"difficulty" : 0.25113525,
"previousblockhash" : "000000025cb702b64c9f44a96ab1f0177c82c203e2dba288423c8abaa7f939ee",
"nextblockhash" : "00000001219aabf7a0c0e629bacf6b70cbd857ebeb7e2575c6049c70306b5190",
"flags" : "proof-of-work",
"proofhash" : "00000000dfa28f824f3c569dbe8ae78c6dd0bb659f084f48d6c72a70277fd76c",
"entropybit" : 0,
"modifier" : "dc6c78fb8aaa45f0",
"modifierchecksum" : "dd993608",
"tx" : [
"a7ed902b6a2dee6a5045d277d19b50c77db83d3b4e7ce55cf203ca59a62db8e3"
],
"signature" : "3046022100ea0230879f31cdf498f658b604b1502ee967c0c40bfce5f34daa60bf6220f7b602210 0db1bce696553cebd95a8721a3dd8b865eb71b85000e85842881756ee115868cb"
}
The difference between times of the last PoW block and the one before last is negative. Thus the re-targeting algorithm in use produces negative difficulty. Though, the getblocktemplate RPC call produces some positive target, then the wallet declines all blocks you find.