Exchange Server 2007 “Service Unavailable” on OWA

This is apparently caused by installing important security patches, noticeably anything to do with .Net. It installs the 32-bit version of .Net 2.0 Service Pack 1, where Exchange Server 2007 requires the 64-bit version and will only work with the 64-bit version.

In the Event Viewer it generates an error 2268 or 2274.
The event text includes “ISAPI Filter ‘C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\\aspnet_filter.dll’”.

Fortunately, this one is easy to fix. Look up and follow the instructions give in the “ASP.NET 2.0, 64-bit version” section.

To run the 64-bit version of ASP.NET 2.0, follow these steps:
1. Click Start, click Run, type cmd, and then click OK.
2. Type the following command to disable the 32-bit mode:
cscript %SYSTEMDRIVE%\inetpub\adminscripts\adsutil.vbs SET W3SVC/AppPools/Enable32bitAppOnWin64 0
3. Type the following command to install the version of ASP.NET 2.0 and to install the script maps at the IIS root and under:
%SYSTEMROOT%\Microsoft.NET\Framework64\v2.0.50727\aspnet_regiis.exe -i
4. Make sure that the status of ASP.NET version 2.0.50727 is set to Allowed in the Web service extension list in Internet Information Services Manager.
Note The build version of ASP.NET 2.0 may differ depending on what the currently released build version is. These steps are for build version 2.0.50727.

Then you should find that OWA (Outlook Web Access) and Entourage 2008 support start working again.