Try to unistall and re-install the game, make sure you don't delete your savegame first, of course I don't think that unistall the game would delete the saves but for safety save the savegame folder ;)

Or better foliage, turn the custom packs off.

Kerb93, the issue happens alot, Operand stack overflow may mean you have too many files opened or something? do you have optifine or anything like that? some versions cant open with some mods. So if you have it on, turn it off. Or you should just wait until the next day then everything might be back to normal. My error always gives me texture errors, when i dont have texture packs or recourse packs on. If you cannot turn optifine off, delete it. Also the same with any other, like forge. So try to turn of mods or packs. Thats why it may be telling you "operand stack overflow". Just so your not embarrassed, this is a pretty common question. So dont feel embarrassed. It happens to everyone, and when it happens, dont be afraid, just ask. Ignore the people who make fun of you. I hope this helped! If not, i will find another way to fix this problem. If none of these work, contact mojang or someone in the Specifications or in the team if mojang. If your unable to do so, Try asking someone who knows more than me. And i highly reccomend you to check out my stuff. I would appreciate it! if not thats fine. So yeah remove forge or optifine. Maybe just try contacting others but PLEASE read this.