Please compare hashes (e.g. in debug menu: getblockhash 992148):
When your hash doesn't match, try a restart of the client (see here why). If that did not help: come to IRC (you probably need to apply then the snapshot/bootstrap)
...
992148 - d4e761628389e276ad0d0154eaed3902c48acf828f591ca207efc8d05f3e70f3 (134.6 mio net weight)
991831 - 48cb05d2b4618344f7d1710d56286415e187a81259937cc7d6c352cecb98e3ac (132.7 mio net weight)
991818 - 62039911acfca61b170cf07bd6643358ffdd225b0663299c300ab4ca78506d6c (144.5 mio net weight)
991808 - 17bc5f71c183066b36546d030658c0c9facf0e6279a7c60b8d6e0a6ea273dd96 (151.3 mio net weight)
2 users report being on a fork with about 31-48 million net weight
which is a quite strong fork
he has wrong hash for 991728 with b076cf43db1493d706c52cd6edb05ff8a7a12c5696bbcfd41e4fc782f791f7ed (correct hash is 566e244b963d9fa99c31d1dd4b2ddf0720db5acd1988f3f97bb7f0d8e6cab1fd) which means the fork took place about 2h ago
his hash for 991727 is correct: 647a4e874f29df46e7b41c7919572dbbac9b92155238ff8c3a105a318681803a
checked some block explorers, but they seem on the "good chain" which has currently >150 million net weight
both users tried a client restart, BUT it did NOT help (both use new version 3.5.9.9)
Please compare hashes (e.g. in debug menu: getblockhash 992148):
most uptodate in IRC!
read in #10 how to check your hash, general info on forks, etc..
see category fork for other fork situations