We are running Exchange 2010 with 2 DB servers and 2 Client Access servers(CAS). We are using the Microsoft software NLB (network load balancer) in front of the Exchange CAS servers.
We have Luminis 5 and are using the pickup.html method.
The issue we are seeing is that SSO only seems to work on one of the OWA servers at a time. If you happen to be directed to the non working OWA server you are presented with the logon prompt for OWA.
At first I thought it might be a Exchange CAS issue, but the server that works varies. One day CAS Server 1 will work, and then the next day CAS server 2 will work.