[TYPO3] Feedburner says my RSS feed is not valid

[Marlies C]

I set up my RSS feed according to the instructions in tt_news and it 
works. I tested it by subscribing to my own feed and new items show up 
and the links work. But now I want to run it through feedburner, but 
that tells me that my newsfeed it not valid. This is the feed link I 
have: http://www.mcuniverse.com/index.php?id=23&type=100.

This whole stuff is a mystery to me. I know there is just one small 
thing that is wrong, but what I have no clue. How do I make my link valid?

Thanks for any input.

Marlies
www.mcuniverse.com