Test Case 8. Fast User Switching support mandatory or not?

It is not very clear in test case 8 if the fast user switching support is mandatory or not.

In the verification part it is written: "The application launched and is able to perform the operation without crashing by both users"

And in the notes part : "If application does not support concurrent user sessions, it must pop-up a message indicating this to the User and write a message to the Windows NT Event Log in order to pass this test case."

Displaying a popup message explaining the application does not run in concurrent user sessions is not the same as "being able to perform the operation".

I do not want to support Fast User Switching, because instances need to communicate in order to work well (they share the same usb peripheral). I have discovered with Vista that it is now impossible to create a global file mapping without privileges or when not running in session 0 (and contrary to XP and 2003, on Vista, first logged user is not running in session 0). I know that I should handle this problem with a service, but writing a service and managing its installation/update/uninstallation adds too much complexity.

Therefore, I would really like to be sure, it is OK if I detect a concurrent user session is trying to launch the process, and to display a warning messagebox indicating this (+writing message in Event log).