Active X Plug-in problem

Some one help me. Whenever I try to play a video file from the internet, ActiveX screws up and closes my browser. If I turn off ActiveX Controls then the browser wont close but the file wont play either. What the hell? please help thanx.

This message comes up when I try to stream videos from the internet using Mozilla Firefox:

"Illegal Operation in Plugin"

Windows Media Player Plug-in Dynamic Link Library

The plugin performed an illegal operation. You are strongly advised to restart Navigator.

Can someone tell me what to do besides restarting the Navigator cuz that doesn't work?