Have you got the apache config? Because it looks like your vhost or directory might be wrong, either that or you've an .htaccess file that is doing that. Why is /kb/ajax.php even being requested? Weird.
Why is someone on vodafone.de requesting your robots.txt file repeatedly? Normally only a search engine would do that, but they generally tell you it's them via the user agent string, which is missing from your logs.
The AH00128 errors are simple "file doesn't exist" errors, likely apache looking in the wrong place, or the file isn't there.
AH00652 is a mod_actions "file doesn't exist" error.. not sure how you're triggering that one. But it makes me suspect the Apache config.
You've done something to it though, because that's not a standard Apache log.
Heck, it could be as simple as mod_rewrite not having a base url set..