A click on the MB1 button with the pointer in the root window (background
picture) should popup the `Workspace Menue' of the Motif Window Manager.
In case this fails one has probably a problem with the mwm Resource
Description Filemwm_rc.dat. Check
whether you have a corrupted mwm_rc.dat in
decw$user_defaults.
whether the resource Mwm*configFile points to a corrupted file.