Problem with setting key on Intuos 4 Grip Pen

[Cam Sykes]

I upgraded to an Intuos4 a few days ago, after having an intuos3 for about 4 years. I have a problem with setting keys on the pen. With my old Intuos3 I could set the 'trigger' button of the grip pen to Erase and it worked well, and even while holding it down I could change brush size of the eraser. I've tried this with my Intuos4 Grip Pen and it doesn't switch to erase, even though I've set the key. I have the latest drivers and all that, so I was wondering if there's a way to make it work as well as it did with the intuos3 grip pen.

I had a work around of setting the trigger button to 'E' key to switch to eraser but it doesnt work the same, because then I have to set another key to 'B' to switch back to brush manually.