If the error that you are encountering is an "unimplemented trap" this is usually fixed by removing the extension "Open TPT Serial Arbitrator" or "Serial Port Arbitrator." However there are some situations when this will not fix the problem. If you are still having the problem restart with extensions off. Open the control panel, then open extension manager. If you are running system 7.5.x select the extension set "System 7.5.x" then scroll through the extensions and control panels until you find the Wacom Tablet control panel and turn it on also. Restart your computer. At this time it will create the Wacom preferences during restart. When your computer is restarted turn all your extensions back on and restart. This will fix your "unimplemented trap" error. If you are running 7.6.x then go through the same process except instead of selecting System 7.5.X as your extension set, select "System 7.6.X Base" then duplicate this extension set so that you can modify it by selecting Wacom tablet.
A simpler solution is apparently coming. I spotted on O'Grady's PowerPage that OT/PPP 1.0.1 is coming in a few weeks. Its Read Me file states: "The OpenTpt Serial Arbitrator no longer crashes with extensions that open a serial driver during system startup (such as the Wacom Tablet driver)."
Finally, a couple of readers claimed that they were having some problems with their Wacom tablet that were solved by removing PrintingLib or replacing it with a fresh copy.