Installing the rollup update 5 on a machine running Microsoft Exchange 2007 SP1 might cause your Outlook Web Access, OWA, to fail with error Outlook Web Access did not initialize
I have already experienced this error at 2 of my customers on fresh installations and I am surprised I didn't find this error documented at Microsoft (Maybe I didn't look hard enough)
The problem is that, for some weird reason, the installation of the rollup update 5 is removing the Exchange server from the Exchange Domain Servers group !
So if you are facing this issue simply find that group, add your exchange server account to it and restart your server. That should do it!