So I remembered I had somewhere still an OrangeCD installation on another older computer, so I compared the windows registry entries. Under "Computer\HKEY_CURRENT_USER\SOFTWARE\Firetongue\Or ganizer\Discogs" there should be two entries, namely AccessSecret and AccessToken, which where missing at my current computer where Discogs was not working anymore. So I exported the registry entry from the old computer and imported again on the current computer. And yes then it is working again!
I know this not really a fix, but it might help someone in a similar situation.