Do you have a remote switch for it?
If so make sure the router is turned off. The little plastic cover on the switch is over sized so that when the router is turned on it limits the depth of plunge so you can't accidentally bottom out the router. This way if the router is spinning and the lock pin tries to engage metal parts won't go flying.
I just had this experience about 2 weeks ago and started to take the whole router apart and discovered this little safety feature( or pita feature take your pick)
Hope this helped,