Sorry I don't have a better answer, but here is something you might want to try. Download a brand new copy of 2.2.0, unzip it on your computer, delete at your server both /inc/ and /plugins/ folder, then replace them with the folders (and files) from the brand new unzip. Be careful of course of any plugins you've added that weren't part of the distribution - you don't want to lose them.

The idea is to see if you have a corrupted file somewhere. If folder replacement fixes the issue then who cares what file was bad - as long as it's all working now :)

We (provider and I) found out that there is a problem with the Apache-Firewall. Error Message:

[Sat Dec 08 14:56:58 2007] [error] [client 84.62.***.***] mod_security: Access denied with code 403. Pattern match "((alter|create|drop)[[:space:]]+(column|database|procedure|table)|delete[[:space:]]+from|update.+set.+=)" at POST_PAYLOAD [id "300015"] [rev "1"] [msg "Generic SQL injection protection"] [severity "CRITICAL"] [hostname "blog.******.de"] [uri "/admin.php"] 

Now we're looking for a solution that fits my (get b2evo working) and providers interests (security). Any suggestens welcome!!!