RSS-Error after moving to another hoster

Hi everyone,

I’m pretty much out of ideas right now and I didn’t find anything useful via Google or this search here.

I am using http://kongfoos.rakai.de/ as a test hoster so I can test functions and plugins before moving to the original site. Everything works perfekt there.
But when I exported the database and files to another hoster (used by our club – http://kongfoos.de/ ) I started getting an RSS-Error.

Error message:
RSS-Error: A feed could not be found at http://tfvh.de/index.php?format=feed&type=rss. A feed with an invalid mime type may fall victim to this error, or SimplePie was unable to auto-discover it.. Use force_feed() if you are certain this URL is a real feed.

According to http://validator.w3.org/feed/check.cgi?url=http%3A%2F%2Ftfvh.de%2Findex.php%3Fformat%3Dfeed%26type%3Drss the feed is perfectly fine, I got that link after searching in this Forum a bit.

Any suggestions how to fix this error?

regards,
Patrick