Quick response:
I found the root on the incompatibility!
Appropriately, it had nothing to do with threads or anything. I had named a variable with the same name as a module.
My test script let it go, but somewhere in Server.pm it had no strict 'vars';. That caused the script to crash with the AUTOLOAD message.

We were able to add threading to rjay's RPC::XML::Server module using the threads module. This project is moving along.

Thanks!!!!