I got this when I tried to install the source code on Windows Server 2008 R2, and this was an issue with EntLib 4.0 as well. The solution is the same now as it was then, but since I had a new OS install I didn't recreate the fix. I had to add a registry key: DisableMSI REG_DWORD value 0 It goes here: HKEY_LOCAL_MACHINE\Software... The description for this key is here: http://msdn.microsoft.com/e...