How to solve connection problem with JTS and JAS? Error CWOAU0061E

Hello,

I started to test the V.6.0.6 upgrade. The environment is Jazz Authorization Server enabled.

So I stopped everithing and first I run a JAS upgrade with Installation manager.
After this I started JAS and JTS to have a look if all is running well with the upgraded JAS.

But unfortunately I'm not able to connect anymore with JTS to JAS. I get following error:

CWOAU0061E: The OAuth service provider could not find the client because the client name is not valid. Contact your system administrator to resolve the problem.

The JAS itself looks good. I can login with https://devclm.bt.siemens.com/oidc/endpoint/jazzop/registration and get the json.

Any idea how to solve this problem? How can I re-register JTS in JAS? How can I see what is in JAS registered at all? Is there any good documentation in deployment wiki about updating and solving issues? I have not found much which helped me in upgrading scenarios.

regards
Guido