Exchange 2007 Web services display “Service Unavailable” after 32-bit .net 1.1 is installed

This happened to me after installing GFI Mail Security on an Exchange 2007 box with HT/CAS/MB roles on it.

Event logs were
Event Type: ErrorEvent Source: W3SVC-WPEvent Category: NoneEvent ID: 2268Date: 28/01/2009Time: 11:46:53 PMUser: N/AComputer: XXXDescription:Could not load all ISAPI filters for site/service. Therefore startup aborted.
For more information, see Help and Support Center at http://go.microsoft.com/fwlink/events.asp.
Event Type: ErrorEvent Source: W3SVC-WPEvent Category: NoneEvent ID: 2274Date: 28/01/2009Time: 11:46:53 PMUser: N/AComputer: XXXDescription:ISAPI Filter 'C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\aspnet_filter.dll' could not be loaded due to a configuration problem. The current configuration only supports loading images built for a AMD64 processor architecture. The data field contains the error number. To learn more about this issue, including how to troubleshooting this kind of processor architecture mismatch error, see http://go.microsoft.com/fwlink/?LinkId=29349.
The fix is to force IIS to use 64 bit ASP.Net. To do this do the following
Click Start, click Run, type cmd, and then click OK.
Type the following command to disable the 32-bit mode:
cscript %SYSTEMDRIVE%\inetpub\adminscripts\adsutil.vbs SET W3SVC/AppPools/Enable32bitAppOnWin64 0
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
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.
A restart of the IIS services is not needed after this
Alternate fix is
You can also manually modify the Enable32BitAppOnWin64 flag in the following file C:\Windows\system32\inetsrv\metabase.xml. Change it to TRUE or FALSE depending on whether you need 32 bit ASP or 64 bit ASP running. Must do a net stop iisadmin first before editing this then do a iisreset after editing.