This is something which I have not seen in a long time, but after doing quite a lot of custom brush building I kept getting the following error dialogue;
ScriptIO: Data map offset out of range
Quitting Painter and relaunching doesn't fix it, and I had to delete the Painter Scripts.scripts file from the current user workspace to get up and running again. My scripts autosave is set for 1 day in the preferences.
Mac G5 PPC OSX 10.5.8
Painter 11.0.1.43
David
Edit: An alternative solution from Ginger Nielson.