From: Marcy Daeffler on
One Exchange 2007 HUB (not really in play for this but thought I would add)
One Exchange 2003 FE/BE server
One Exchange 2007 CAS server in same site/subnet as the other Exchange servers
One Exchange 2007 CAS server in a separate site/subnet
Two Exchange 2007 Mailbox clusters (active/passive for each)

The below results are the same whether I go to the CAS server in the same
subnet or the one segregated in the other subnet. So apparently I have
something not configured as I have it configured the same one each of the CAS

OWA for 2007 mailbox
https://2007server/owa works fine
https://2007server/exchange prompts for logon then get a 500 Internal server

OWA for 2003 mailbox
https://2007server/owa not supposed to work and does not
https://2007server/exchange works fine
https://2003server/exchange works fine

I have checked to be sure all IIS and WWW services are running on all
Mailbox servers.