2012: SCREENMENU command is undefined by default in AutoCAD
You migrated your settings from AutoCAD 2011 to AutoCAD 2012 and are able to see the screen menu but cannot interact with it because the command is undefined in AutoCAD 2012.
Use the REDEFINE command to redefine the SCREENMENU command:
The SCREENMENU command was undefined by default in AutoCAD 2012 so that CIP data could be gathered indicating how many customers redefined the command and how many never noticed it was missing. The command is still supported, tested, and functional, but it must be manually redefined.