Theres an answer to this. There is a thread somewhere in here about the thin film that connects to the screen has came loose. He just resoldered it.

 

Hello I know this thread is a little old but just want to share my experience so info can be out there for others in the future.

I recently experienced the "external system not connected" and my navigation stopped working. I removed the navigation ecu (where the navigation DVD is) and opened it up. There was some corrosion on one of the board and might have shorted some of the pins. Might be from the humidity? Anyways I sprayed some electronics board cleaner I got from radio shack and cleaned it with a toothbrush. Reinstalled it in the car and it works now.

Conclusion: if you have this error, the navigation ecu is bad somehow. In my case I was able to clean it.

 

interesting. Wish i knew that before I took mine to United Radio to repair.

 

Is the issue fixed? What did they find out?

 

Of course. Don't really know exactly what was done to my unit but the receipt mentioned, rebuilt head-unit, replaced digital cable to master radio, repaired/adjusted relay connector of master unit.

The guys warned me about the afternarket DVD disc saying the paper/sticker is likely to come off after a while from extreme heat so it's likely to jam up the head unit.

Bottom line-- have a 1 year warranty on their work and it took them a day to complete the work. Since my ML isn't the only problem-child they have a testing station that helps them troubleshoot the issues.