Modifying Exchange Server 2007 Roles Breaks Outlook Web Access

Update: 18th September 

I’ve come across a frustrating problem with an Exchange Server 2007 deployment in which Outlook Web Access is not functioning correctly for one of the Client Access servers.

Here is a test scenario in which the problem occurs. 

1. Install an Exchange server TESTEXC1 with the Client Access (CA), Hub Transport (HT), and Mailbox (MB) roles.  In other words, a “Typical” installation of Exchange Server 2007 as many people would do for their first install.
2. Install a second Exchange server TESTEXC2 with the MB role only.
3. Create at least one user mailbox on TESTEXC2.  If TESTEXC1 has an Administrator mailbox you should also remove that or move it to TESTEXC2.
4. Test Outlook Web Access (OWA) via the https://testexc1/exchange legacy URL, as well as the new https://testexc2/owa URL
5. Remove the MB role from TESTEXC1, leaving the CA and HT roles installed.
6. Test OWA again via the /Exhange and /OWA URLs.  There are two scenarios I am seeing here in production and test environments.  In one environment the /Exchange URL prompts you to logon before then showing a 404 error in the browser, but the /OWA URL works fine.  In the other environment both the /Exchange and /OWA URLs show 404 errors after logon.
7. Look in IIS Manager.  Note that all of the appropriate virtual directories for Exchange are present and appear to be configured correctly.  Try an IISreset.  In my environments OWA still fails to work properly.
8. Remove the CA role from TESTEXC1 (setup /mode:uninstall /roles:CA)
9. Reinstall the CA role on TESTEXC1 (setup /mode:install /roles:CA)
10. Test OWA via both URLs.  It now works correctly.

I haven’t been able to find any information online regarding this particular problem.  To me it seems a bit unreasonable to have to remove and then reinstall the CA role to get OWA working again after the removal of the MB role breaks it.  I’m hoping to find a solution to this problem that does not involve reinstalling the role and if I’m successful I will post the outcome here.

Update: adding or removing the Mailbox Server role to a Client Access Server seems to break OWA.  In my tests both actions caused OWA to break to some degree and required the CA role to be reinstalled to fix it.