erase does not work with wacom classic XL

Hi when I try to erase with the pen (eraser side) , the mouse cursor turns to eraser icon but it does not erase, it draws !.
Any ideas ?
btw I am running in Mac OS X

have you checked to make sure you have the latest drivers? If so, go into your tablets settings & make sure everything is configured properly - check the sticky threads for the settings you should have.
hope that helps