Looks like a bug in the forum - that text that you mention is part of an error message sent by the forum instead of the actual RSS feed data that the reader is expecting.

I was able to repeat it over here if I try to get RSS data after doing a Logout of the forum.

Looks like it works ok after that initial error though. So for now just don't hit that logout button and it may work better. Some time in the future I'll try to take a look at what is causing the error, but it will probably be a while. Something to do with the forum being confused if you are logged in or not.

- Michael