Exchange 2010 Outlook Anywhere not working - RPC Proxy, Address Book?

Solution 1:

This was a stupid configuration Heisenbug of some kind. The registry was configured properly for RPC, and the problem was not specific to the OAB, that's just the first thing that's checked. It took a reboot of the CAS servers to get it to work.

Further, the real root cause was that I had recently installed a third CAS server as a test, not in the array. I fed it dummy values for public URLs that weren't reachable, and for some reason (wish I knew) those got written into Autodiscover. I uninstalled the CAS role from that test machine and it cleaned up autodiscover, but still had trouble with RPCPing until the reboot of the remaining CAS servers.