User exit code does not execute

I'm having a problem with User exit code that does not execute yet seems to be set up correctly.

The User exit is implemented as FM "EXIT_SAPLIPW1_001" in function group XQSM.

I've tried everything I know of with the CMOD and SMOD transactions, and I suspect some sort of transport error.

The only clue I can find in comparing the development system (which works) with the test system (which does not work) is that running "Extended Check" in SE80 on function group XQSM fails with the following error:

"The namespace of program SAPLXQSM has the setting "C" and cannot be tested."

Has anyone any idea what could have happened?