Poloniex recently did a software upgrade and they're currently experiencing issues.

I just got this in an email:

"As part of our efforts to improve the site, we are conducting maintenance beginning on February 22nd at 22:00 UTC. We expect the maintenance to take several hours. During this time, the site will be offline and trading will be suspended. Your funds will be safe during maintenance, and you do not need to do anything at this time."