[MLE]

First of all, what type of wacom do you have? Graphire, Intuos, Bamboo? It should all be the same really, but go into your pen tablet settings, and you check to make sure that the buttons are set properly.

If it is an intuos or something similar enough, you might have two tabbable buttons on the top or something that say PEN and MOUSE. It's possible you tapped MOUSE with your wacom pen, and made it so your tablet thinks you want to use the pen as a mouse. The first time I accidentally did that, i freaked the fuck out.