I've read about quite a few people who've had issues with Cryptopia, but I have to say I haven't had a problem so far. I traded a few thousand ETN way back on the day it launched on Cryptopia for a nice profit, although most of that is still sat in Cryptopia, as it seems to be when people try to transfer coins out that they get issues.
They're doing a really good job, regular communication, true to their original stated goals. Hopefully the price will reflect all this soon!