It happened to me too because my cd was scratched so you should send maxis an e-mail to get a replacement cd. next time you should copy your expanision that you installed last on a cd so it dosen't happen again. I HOPE I HELPED!
LOL I'm glad I read this. I thought by installing Stray Away it would just work on it's own. I've been wondering why those varments were still getting into my yard.