R56 Data loss
 

Hello all,
08 R56 S with navigation and convenience. Here's my problem. I walk up to the car and push the button on the door handle to unlock the doors, and nothing happens. I pull the key fob out of my pocket and use the remote and the doors unlock. I start the car with no problems and notice the data under navigation has been erased ie: average mpg, average speed, also the time reads 00:00. This has happened 4 times in the past 3-4 weeks. It's as if the battery had been disconnected, but it only affects a few things.It happened again today. The date and radio presets were not erased??? I'm a little baffled how the clock would reset but not the date? And how the door locks are related? Is there a common power/ground lead that I should start looking for a loose or corroded connection? Any ideas?
Thanks in advance
Toby