Error 500 on trying to subscribe to blog RSS

Hello,

URL: http://3pm.nu/

When I click on "Abonneer op feed" (Subscribe to feed) I get sent to the following page:
http://3pm.nu/?format=feed&type=rss

Which contains a 500 - Unable to load renderer class error.

Can anyone please look at this issue for me?

Thanks in advance!

Bjorn Elsing



And another, not relevant, question: Is it possible to have a visitor subscribe automatically after they've placed a comment on a blog?