The Missing User Provider warning is issued in the following situation:
Could not find the '<provider>' User Provider eSpace in this server. Application runtime errors might occur: your eSpace has a User Provider eSpace that does not exist in the Platform Server you are publishing to.
Do one of the following: Check with the Service Center administrator or with the User Provider's owner to determine what the cause might be for this situation; or change the User Provider eSpace property of your eSpace.
Single Sign-On | About Warning Messages