We recently upgraded some Unity servers from 4.0 to 5.0. Everything went pretty smooth but we noticed that MWI is problematic when the primary server fails over to the secondary. I noticed in the integration manager that the subscribers and call handlers were assigned to the primary integration during normal situations, and the secondary showed the subscribers and call handlers as unassigned. When I fail the servers over, the MWI quits working. As soon as I fail back to the primary, I get MWI.
I believe it is related to the fact that the secondary server shows the subscribers and call handlers unassigned to any switch type, but I don't know how to make them assigned. If I manually assign them, then they are unassigned from the primary.
I'm not sure if this related to the 5.0 upgrade or just a previous mis-configuration of the failover.