Thanks for all your replies, i tried
uninstalling amule, then
- i checked /usr/share/amule/* (webserver directory was in there, after uninstalling amule it was empty, so it's contents were up to date after reinstalling)
- i checked /usr/local/share/amule/* (didn't exist)
- i tried a find / | grep -i amule, and deleting all that belongs to it (wasn't too much except for the amule profile directory)
I also deleted the amule profile in my home directory and did all configuration from scratch...
--- and it didn't change anything ---
The strange thing is: All the pictures except those for the progress bar are accessible and work fine! Also, the aMule.tmpl file is accessible, since if I rename it, the webserver doesn't work anymore.
On the console where i had started amuled, i once in a while also get errors like this:
22:42:03: Error: can't open file '/usr/share/amule/webserver/default/%EF%BF%BD%EF%BF%BDfa%01%13/emule.gif' (error 2: No such file or directory)
I really don't understand this...

How can it come up with such a File Name? Might this be a Unicode Problem?