Stuck on block 278763 using new nodes.... just happened too.
I am stuck on block 277928 with 3 connections. I solo mined for days on 4 connections. then I noticed that the pools were mining at a higher diff and taking longer to find blocks. Now I can't sync the client. I hope i am not on a forked chain I mined 100k plus CDC already.
I'm afraid you may be on a private forked chain, with your own low diff - it's unlikely you'd be able to mine roughly half of the entire money supply over that 4 day period.

Current block on the two seed nodes is 280798. Both pools are on the same chain & block.
edit: I'm preparing a pastebin with a list of block numbers, diff, hash etc so we can figure out if/where you forked.