What is exactly the difference between a client and a cp user? When creating a client a corresponding cp user is created. When creating a cp user no client is created... Meaning this cp user is not aware of any client limitations... what is its status?
A CP user is the login for the client. This is splitted to enable a client to have more then one Login, e.g. when company has more then one administrator. Then you missed to add the client to the group of the CP user.