Just to let you all know that after trying all of the above suggestions, I found that for some reason the problem was being caused by a corrupted neighbourhood. Simply removing the offending folder didn't do the trick though, I ended up having to back up my downloads, delete the entire EA folder from My Documents and letting the game generate a new one. Oh well, at least everythings working again now, but guess who's gonna have to restart her prosperity challenge
Thank you everyone for your help