I now have an extra icon om tje sys-tray leftover each time I start DM and close it. The icon's properties tell me its for DM 4.7 (I'd installed 5.0 over it.) Also I found this
Desktop Manager MSI missing !! - BlackBerry Curve - BlackBerry 8300 Series Smartphone - BlackBerry Support Community Forums
Now, if you follow RIM's advice from the link embedded in the above thread, to fix all this you have to completely uninstal 5.0, loosing all your settings, clean the registry and start all over again.