Adding new server to existing User Source fails

I have a eDirectory User source where i want to Add a new connection, in order to remove an old server later. The 'new' server is an OES11SP3 server, and handles the master replica of the other two servers (r/w) in the user Source. However, when i want to add the server i get the following message:

The wizard cannot continue for the following reason(s):
Error The connection specified does not belong to the same directory as the selected authoritative source.

I have looked at the LDAP certificate's, if there's someting wrong, but i can't find a clue what's wrong. Anyone any idea's?

ZCM version