Hi Low-high,
Thanks very much for your help. I got it operating again though I am only 99.999% sure what exactly did the job. I had CCcam 2.1.0 with CCcam.cfg 'SECA HANDLER: 1' on for hours without effect, then I switched to 2.1.1 with CCcam.cfg 'SECA HANDLER: 3' and instantly it operated. Coincidence my re-activate code just came by?

To help others I describe the problem and solution here. I think it applies to any system combining a Canal Digitaal card with CCcam.

Problem: Some (1-2) months after replacing the old Canal Digitaal card with the new Mediaguard 3 (SECA 3) card decryption of the canal digitaal card stopped working on my DM500+ (probably applicable to other systems running CCcam too) using CCcam. Looking at the card info / entitlements (http://<IP of my dreambox>:16001) one can see the line "006a CANALDIGITAAL : <date>". The <date> field is in the past effectively meaning your card was not updated like it should.

Solution: Add the line 'SECA HANDLER: 3' to your CCcam.cfg, restart CCcam, using the canal digitaal website re-activate your canal digitaal card (like you would if you have left your receiver off for a long time). Maybe you want to switch to the latest CCcam (For me 2.1.1 worked)