The Session &1 and the Role &2 belongs to different sites. The Role can't be added to the Session.
&1 - The session ID
&2 - The name of the role
An attempt has been made to add a role to a session. This has failed as the role and the session belongs to two different sites. This will normally be caused by an call to the Session.AddRole API.
The developer responsible for the business process must ensure that the roles assigned to a session belongs to the site used by the session.