Hi Walter,   I also keep getting a message saying "The system can't execute the navigation program".    I reloaded 6.5.6 and still get it..    I unplug and reboot, and it comes up..    This has only happened since my update last week...   I'll give it a try tomorrow and see how it goes...
It also seems that my connection on the board may be loose.   When I plug it in to the power supply at home, any movement will force a reboot...   I'll send this information from help page..
 
Wade Leveille