Tony, wellcome to forums.
I have no problems with the Screen Saver and avast.
What screen saver are you using?
Are you using it ‘with’ avast screen saver or not? I mean, does avast ‘load’ your screen saver while scanning?

What do you mean with ‘crash’?
Is your avast updated? How do you connect the Internet: dial-up or DSL?
Did you set this into the avast settings (Update (Advanced))?