I know this thread is old, but this may help others. The problem actually may be in the interlock system which maybe stuck. The interlock plunger is a flat bar that moves with the switch lever and engages the interlock disc on the shifter shaft behind the plate. When you remove the switch plate assembly as mr. fixit  suggests above, check to see if the gear lever moves and check if the interlock plunger behind the plate is out of position locking the shift lever.