The weird characters are because of "Content-Encoding: gzip" - it's a gzip compressed response. It is normal that it looks that way.

I don't understand the connection with your comments feed though.

What's the URL of your comments feed?

I was not sure if the weird characters had a connection to the problem.

One feed for posts is here:
http://blogit.oamk.fi/alumnit/?tempskin=_rss2

That works fine.

But this comment feed gives an error 500:
http://blogit.oamk.fi/alumnit/?tempskin=_rss2&disp=comments

If I change debug mode to '2', I can get this out of it:
http://tny.cz/270f11bc

I'd like to see the real error. Turning on $debug generates nothing but noise at this point. What you want to see is the original error message that PHP produces when generating the 500 error. You don't want to turn on b2evolution debugging but PHP error messages.

Sorry for the late reply.

I managed to get the problem fixed. The problem was that I had old versions of comments.main.php files in /skins/_rss2/ and /skins/_atom/ folders.

After I upgraded the files from 4.1.6 the problem was fixed.