I'm having trouble with my bamboo pen?

It most likely isn't from the pressure sensor, because the nibs wouldn't fit if there was something wrong with it. Because the eraser is working, it's most likely a software issue. I'd unplug the tablet, uninstall the software and reinstall it, then make sure to plug the tablet in AFTER (a common mistake that causes the Bamboo to behave erratically) everything is completed. Your Bamboo should be returned to normal. (: