The responses by MikeTangas and md21722 would be a cure to the situation...I have had experience with this and one or the other solution would work.
Usually if the light is about to burn out and you can jiggle the bulb back on, the indicator light should go out. If it doesn't, then the metal track inside your taillight housing(s) has indeed shifted enough to prevent one or more bulbs for getting a solid connection with the associated sockets. That would change the total resistance enough to fire up that dash light (which, btw, is exactly how the system determines that there is a problem).
You can usually press against the track firmly with your fingers near the area that your back-up light bulbs reside, and then try again to see if the dash light goes away...
2009 ML350 (84K) - Family vehicle
2001 CLK430 Cabriolet (71K) - Wife's car
2005 BMW 645CI (124K) - My daily driver
2012 Mustang V6 (60K) - Daughter's car