If you turn the locker switch off, then key off and back on, it may stop complaining until you try to use it again. If it is stuck mid position this won't work and your best bet is to pull the motor out.
If you are DIY inclined, it is very easy to pull out the motor from the rear differential housing, IIRC it is just 1 or 2 bolts. Once you remove it, you can see if the motor spins, and move the locker mechanism by hand to get an idea of where your problem lies. You should also be able to get the motor and differential into fully open position, which should get rid of your flashing light, unless there is an electrical problem.