Message "P R O D" on a mercedes audio 10

The car radio plays for about 30 seconds, stops playing, and then says : "P R O D" on display.
This does not look like a queston for a code, it does not accept any push on the buttons.

I can put it off, and then on again, plays 30 secs, and "PROD"...
Thanks, Marc
What's on Shortwave guide: choose an hour, go!
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
Add image file
Upload is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.