A THREAD FOR NEWCOMERS!

It kicks me out of the game when I launch it with a mod, and it says that there's some file issue and to send an email to the developer. I have the Complete version, and I'm using Windows XP. 1. What can I do to prevent it from kicking me out? 2. Is it possible to play online if my friend doesn't have the mod installed, but I do (I know that HD+ is required for everyone, but I'm just wondering about playing with just HD)?