Code:
Warning: call_user_func_array() expects parameter 1 to be a valid callback, function '' not found or invalid function name in /var/www/web40/htdocs/......./admin/load.php on line 39
Looking at that line 39 seems you have a problem with a plugin. Did you delete it but is it still there in your calls ? Changed a name or path maybe and now it cannot be found ? Deactivate all plugins one by one and see what happens.