Does it work when you use the menu link to call uddeIM? In that case it might be a problem with the CB login module.
Does it work when you disable sh404? In that case its a problem with sh404 and you have not to check Joomla and uddeIM setup.
Maybe the CB login module uses the wrong Itemid (e.g. uddeIM gets this ID from the jos_menu table). Usually 3rd party SEF components do not work when this ID is not correct.
Another problem (very seldom, but seen on very cheap mass hosters and self configured dedicated servers) might be that your server dies while executing the php scripts, because of e.g. not enough memory or execution time for the scripts. In that case increase these values in your php.ini.
uddeIM & uddePF Development
CB Language Workgroup
CB 3rd Party Developer