The February 7 issue of Info Alley posts the following advice:
"If you install Mac OS 7.6 on your computer with a Wacom tablet, make sure you have the latest Wacom driver version 2.5.1 and remove the OpenTpt Serial Arbitrator from your system. Wacom has an extension called SerialDMA which replaces the OpenTpt Serial Arbitrator."
MacFixIt had previously reported this problem as one that also affected System 7.5.x, but only the serial port version of Wacom tablets.
Wacom has a web page that covers other conflicts you may have.