I ran into a very interesting 32/64-bit problem the other day that looks to me like Microsoft has goofed. The issue involved installing the x64 version of WSUS on Windows 2008. In Windows 2008, WSUS is now a feature and can be installed without a download.  During setup of one of our new customers, WSUS was installed on an x64 Windows 2008 server that was currently hosting some .NET web services in IIS. After the install of WSUS, the web services would return a 500 error for every request. The error page noted a problem with DynamicCompressionLibrary. After much digging, the problem was caused by installing the x64 version of WSUS alongside x86 web applications in IIS. [more]

When WSUS is installed, it installs a dynamic compression library called suscomp.dll globally in IIS. This compression library is used to compress updates before they are streamed down to clients via BITS. However, due the inherited nature of .NET configuration (web apps inherit global settings in IIS), these .NET web services were looking for the x86 version of the suscomp.dll (search path is by default at c:\windows\SYSWOW64\) which WSUS DOES NOT install. It installs the x64 version (default path at c:\windows\system32\). Without a matching suscomp.dll compression library, the inheritance chain is broken, and you will get 500 internal server errors. This could all be avoided if Microsoft would just include the x86 version of suscomp.dll in the install of x64 WSUS. The fix is to find an x86 version of suscomp.dll (from another install of WSUS) and copy it to c:\windows \SYSWOW64\ and do and iisreset. Thanks Microsoft!