Try this first before clean uninstalling/reinstalling - go to Synchronize - Configure Tab - Reset Sync - try again. If not, then try changing USB ports on your PC (where the USB port was originally connected to, change it to somewhere else) - try again. If still a problem, unplug your USB cable from the pc, disable the RIM VIRTUAL Sieral Ports on your PC, restart it, restart DTM, replug the USB cable, replug the BB again and try again. Give these steps a try BEFORE removing/installing DTM again.
Hope this helps.