Issue

Can’t install WSUS 3.0 SP2 (Windows Software Update Services) on Windows Server 2003 64-bit OS.
Following error is displayed during setup:

The error indicates that IIS is in 32 bit mode, while this application is a 64 bit application and thus not compatible.

Resolution

Issue is caused by ASP.NET 1.1 running in 32bit mode as it doesn’t have 64 bit version. To resolve the issue we need to switch to ASP.NET 2.0 64 bit version. To do this perform following:

• Open command prompt and run following:
• cscript %SYSTEMDRIVE%\inetpub\adminscripts\adsutil.vbs SET W3SVC/AppPools/Enable32bitAppOnWin64 0
  (Disables 32 bit mode)
• %SYSTEMROOT%\Microsoft.NET\Framework64\v2.0.50727\aspnet_regiis.exe -i
  (Installs and enables 64 bit ASP.NET 2.0)
• iisreset