[UPDATE: see this new post here Custom Trust Level For Community Server]
I just installed Community Server 2.1 SP1 for a client. I had been told that it would run in Medium trust, so I tried that setting. Unfortunately, in Medium trust, adding feeds gives the following error:
The problem is the same as discussed a while back in this thread. And apparently it was not fixed in 2.1 or 2.1 SP1.
Here is my solution:
In web.config, I added this element to <system.web>