Yahoo messenger webcam broadcast problem

I get the message ''webcam does not support required image size'' when i try to run it on ym.
I ran the video and audio test under my messenger>preferences>video and call settings and it worked perfectly there, i can see myself, but once i tried to broadcast i get the above mentioned message. my webcam is A4 TECH PK750-MJ. Its a plug and play but i have installed the driver too. one more thing, the camera source under webcam setting does not show my installed A4tech or any USB video device, only Microsoft WDM image capture (win32)