My Bamboo Pen is messing up?

I bought a Bamboo Splash tablet about a year ago, and at times it doesn't work correctly. The computer will recognize the pen and have it move, but when I try to draw on Paint Tool Sai or CS5, the pen's sensitivity is gone and when I draw the pen stops, shows the loading circle, and turns into the dropper tool (On Sai, while on CS5 it'll open the pen/brush's options). I uninstalled the dock. I've updated the recent drivers and Air But it still doesnt help. I have to to hope that every time I plug it in that it works! And if it doesnt I have to restart my laptop at least once to get it working correctly. I should also add that sometimes when I turn the computer on, a box will pop up and say it cannot find the driver (but if it does or doesnt Im not sure if it affects if the tablet will work or not).