Can you tell me whether you're using MacOSX, or Windows (Vista or XP)?
You can reset ArtRage 2.5 to its default settings by doing the following:
As you start ArtRage, hold down the spacebar key on your keyboard. ArtRage should start up full-screen, and check for updates. All the brush and paint settings will be at their defaults.
If that doesn't cure your problem, you should ensure you have the latest drivers for your tablet.
Let me know if you still have problems and we can try some other things.
AndyRage's mantra for graphics engine code:
"Sure - how hard can it be?"