I'm having similar problems, check my previous post. Though, it is funny that after I posted about problem and restarted
computer my miner got 2 blocks in few minutes both with 92/82 difficulty hashes! Could it be Java is acting up somehow?
I'm using NXT as well and I noticed that when registering aliases Java tend to stuck and not respond for some time. All
other software I've been using that use Java were running into sync/keep alive/connection issues. MultiBit comes to mind
as main candidate, using it was a horrible experience, totally not recommended.