I recently added a new server to my company's org. After installing Exchange 2003 and SP2 for Exchange, I ran Microsoft update and brought everything up to date and started moving mailboxes across to it on that night. The next day I started getting complaints that OWA was not working for some users. I quickly realised the affected users were all on the new server. I checked and all of the IIS websites were configured in the same way, and the HTTP server in ESM was set up identically across all servers. After rebooting the server out of hours and resetting the IIS websites, I made a small amount of progress and via the front-end I could get it to start loading 'basic version' before giving up half way through. This is how it looked:

Not very pretty eh ... Going directly through the back-end though, it worked perfectly.

After some more investigation and following a hunch, I moved my mailbox to a test server (where my mailbox worked through OWA) and started looking at Windows updates that were available for the test server, that were already installed on the new server. Through some testing I eventually found that if KB911829 is installed on the back-end but not the front-end, it will break OWA for users on that server. The fix is simple - remove the patch, or update all the Exchange servers with the same patches.

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