What mouse are you using. I have had this happen to me while playing UT2003 with my Logitech Wireless mouse. It autofires, then the receiver resets and I can't move. Maybe it's just me that is experiencing these problems.
Try with different mouse.
That is all I can think of right now.
its the microsoft wireless explorer i installed current drivers and i also found at lower res it doesnt happen as often but once is unacceptable, cus i cant take chances in scrims and stuff so could it be my 9700pro i just got it and this is when it started, i got the old drivers for it cus the new ones dont work with cs, but could it be anything else ? is it cus i have the mod version not reatial ??