game fails to load when entering live mode

When I try to move a sim into a lot or play as a townie, the game shows an error message that is something like 'Game failed to load. Error code:(i don't remember). Recommend restarting the game.' 

I restarted the computer and tried to play as a townie but the same error code appeared.

I use cc and mods, but they are all up to date. Does anyone know how to fix this?