Problem after Installation (2.6): Warnings and Fatal Errors

After installing the newest version (no upgrade, fresh installation), i have a problem.
If i want to open existing articles (sites work) in the admin panel (to change them or so…), i get this reports:

Warning: ini_set() has been disabled for security reasons in /usr/export/www/vhosts/funnetwork/hosting/cyone/weblog/wp-includes/pluggable.php on line 1517

Warning: require_once(Text/Diff/Renderer.php) [function.require-once]: failed to open stream: No such file or directory in /usr/export/www/vhosts/funnetwork/hosting/cyone/weblog/wp-includes/Text/Diff/Renderer/inline.php on line 17

Fatal error: require_once() [function.require]: Failed opening required ‘Text/Diff/Renderer.php’ (include_path=’.:’) in /usr/export/www/vhosts/funnetwork/hosting/cyone/weblog/wp-includes/Text/Diff/Renderer/inline.php on line 17