Hi Zmsil,
This looks like it might be a bug with the community version of RM you are using. I'm guessing from the stack trace that despite being 'admin' .. CMIS is trying to make a call on a RM artifact with a method it's not allowed to use.
This is because the normal entry voter is bypassed when dealing with a RM artifact in favor of the RM Entry Voter. This voter looks for the RM related method level security and if none is provided it will default to DENY. So I'm guessing this is what's happening here.
This has been resolved in the most recent 2.1 community drop .. which has a much more configurable way of extending the RM method level security checks if something is missing.
There is probably a way to bypass this check, but you will need to delve into the code. Alternatively I'd suggest moving to a more recent community release, the latest being 4.2.e, which has a far more feature rich and stable RM offering.
Cheers,
Roy