Error code 13 on The Sims 3?

Hi I've been experiencing error code 13 a lot on The Sims 3 lately (I've had the game since '09, I don't have World Adventures or Medieval or any expansion pack), I've experienced error code 13 a little bit in the past, I always just went to edit town and then changed something and then it was fine. Recently, that hasn't been working, also I experienced error code 12 once and there was no solution to that error. Can someone help me/tell me why it's happening? I have a lot of custom content and one world I play a lot is really full, so that's probably a reason why. Is there anything I can do to avoid these errors and not have to delete anything? I already deleted a lot of other saved worlds and saved sims!