[Mediawiki-l] preferences

[Scheid, Bernhard]

Hi,

I am presently experimenting with setting up a wiki for educational purposes. Everything went fine so far, but when I try to change my own (Sysop) preferences I get the following error-message, whatever I try to change: 

Warning: require_once(/u/www/bescheid/w/skins/monobook.php) [function.require-once]: failed to open stream: No such file or directory in /u/www/bescheid/w/includes/Skin.php on line 139

Fatal error: require_once() [function.require]: Failed opening required '/u/www/bescheid/w/skins/monobook.php' (include_path='/u/www/bescheid/w:/u/www/bescheid/w/includes:/u/www/bescheid/w/languages:.:/usr/share/pear') in /u/www/bescheid/w/includes/Skin.php on line 139

I am not aware that I changed something relevant in LocalSettings.php, and monobook.php exists in the skin directory. I did make some small changes in monobook.php (adding HTML tags), though, but since all other pages work well, I do not understand the reason of this error. 

Many thanks in advance

Bernhard