In William Thier's excellent SSC article "Configuring Database Mirroring" ( http://www.sqlservercentral.com/articles/Database+Mirroring/72009/ ) he mentions...
"If the mirrored database contains non domain users, SQL_LOGINs should be created on the mirror server with the same sid as the corresponding login on the principal server"
We have a Login on both our PRINCIPAL & MIRROR, created by the SQL Server 2008 R2 E'prise installation, called ##MS_PolicyEventProcessingLogin## --- with different SID's.
Does this Login need to be sync'd on the MIRROR w/ the same SID?
BT