Try changing the graphics setting (Fancy to Fast in menu) or increasing the in-game fog (Hitting "F"). I know of a few people that need to have fog around the middle setting, too far and the game crashes for them.
COLL1N posted... Didn't work. I honestly don't see how I can't play this game seeing as how I can play dragon age with maxed graphics...
I've never had any problems with this game and i havent encountered any bugs in single player. Are you trying to play Alpha version? Classic? browser? downloadable version? multiplayer?
My pc specs: Windows 7 64-bit, ATI HD 5870, intel i7-860@2,8ghz
So if you're using windows 7 64-bit the problem isnt from that... Do you have the latest Java version installed?
and btw even with my computer the framerate still drops sometimes even though the graphics are pixelated it still draws everything very far if you have render distance set to far and its in development so cant really expect perfect performance from it yet.
You should also google your error or something that might help.