Hello, Im using photoshop for a while with my genius mousepen i608x and i didnt really use the pen buttons and everything worked fine for me.
But today I dicided to try it and I assigned to my button 3 a function UNDO and suddenly all my pen does is erasing , when I take a pen away off the board my functions works fine with mouse I can zoom brush and erase, when I put pen on the board it still shows which tool im using for example brush.. but my pen is only erasing, even when using zoom... I reseted settings in photoshop and in genius , nothing helps.
Its sounds more like an Operating System or Genius problem than a Photoshop issue.
Have you reinstalled the Tablet Driver Software ?
That's the first thing I would do - then if that doesn't work you can look further.