I Am having the same problem with an R300 see todays posts, also this has been reported beore on this forum only recently- but a search did not turn up the page so I am still looking.
Iam wondering now if this colud be some new form of nasty?
Have you for example downloaded a revised driver?
Are your running XP wiyh SP2 inplace?
Take a look at my R300 post .
It may be a good idea to workk this one together