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.
Somebody?
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
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