This issue has been fixed with the System Update 3.0 from Apple.
When running ClarisWorks 2.1(up to and including 2.1v3) in native mode on a Macintosh 680xx machine with a Power Macintosh Upgrade card, using the Communication Environment will cause a system crash whenever a menu item is selected.
There is no workaround in the native version. The Mac 680xx version in emulation does not exhibit this issue.
The issue lies with the Apple Comm Tool Box, and has been fixed with System Update 3.0 from Apple.