I had similar problem to that reported in the thread "Pressure Senstivity" .
For me the pressure sensitivity suddenly, for all tools, became mis-scaled in the sense that to make a dark mark, I had to rub a tool back and forth many times. I guess that a better way to put it is that pressure sensitivity for all tools suddenly became stuck at some very low value.
I did find the .prs file and deleting this and restarting Art Rage did solve the problem. I am using the full version.
I do not know if this is relevant, but before this occurred, I was using multiple layers and had incorporated a tracing image into the current layer
If this anomaly re-occurs, would it help if I sent Ambient Design the .prs file before deleting it?