Then you should ask yourself this question:
"Is SSO / Spnego / Kerberos working on the Media Manager??"
The document about enabling SPNEGO on ST 8.5.2:
But when this doesn´t work, and you get the above mentioned error code, then there is in fact a different way of testing if SSO works on the media manager.
As there is no Media Manager URL that can be protected by SPNEGO, the best way to test whether your media manager is working is to log in to your Sametime Connect client and confirm that AV can be seen in your Preferences and that you are able to make AV calls.
You can install the snoop application (DefaultApplication.ear) and deploy it on the mediamanager server. And then try the url http://media.company.com:9080/snoop (portnumber may differ in your environment)
If you get prompted with a login box, then SSO is not working. If you get to see the info of the Snoop Servlet, then you´re good to go.
I got the errormessage AVKCS2200E because the media manager in fact did not have SSO enabled, but both the proxy server and the meeting server did have it enabled and working.
After chatting with IBM about it, they said that the only PMR that has this failure code related to it was about errors in the Sametime Bandwidth Manager. (Thanks Nicolas)
But in my case, no Bandwidth Manager was installed....
Lovely! No pmr needed :-)