What are some of the reasons that the Quit command would be ignored?

I have a form where an error is happening in one of its methods. The form itself has no code in the error method. I have an On Error handler that is being called. It logs the error and for this particular error has:

On Shutdown Quit
Quit

The next thing I see is another error on the next line of the form method, duly logged by the error handler and which also should QUIT.

This system is a mashup of SPRs and forms, so I suspect I'm not clearing something in the error handler that should be cleared before quitting. The call stack has 2 SPRs, and a PRG that calls the form and then does a Read Events.

Any help appreciated.

June