Resolution: You may receive this error if you do not have the required prerequisites installed. Before installing a hotfix please review the prerequisites section of the hotfix knowledge base article and confirm that you have the proper operating system service pack or .NET Framework service pack installed.
The service pack pre-requisite can be found in the "File Information" section of the KB article. Make sure you are on the required OS service pack level as well along with the .net framework pre-requisite mentioned in the article.
Here are a couple of hotfix article with specific prerequisites:
FIX: A System.InvalidOperationException exception occurs when you use a WCF client proxy that is generated by the ServiceModel Metadata Utility tool from the service metadata that is in the .NET Framework 3.5 (http://support.microsoft.com/?id=976814)
You must have the .NET Framework 2.0 Service Pack 2 (SP2) or the .NET Framework 3.5 Service Pack 1 (SP1) installed to apply this hotfix.
For all supported x64-based versions of Windows Vista SP2 and of Windows Server 2008 SP2
FIX: URIs in a WCF WSDL document refer to inaccessible internal instances instead of to the load balancer as expected in the .NET Framework 3.0 in Windows Server 2003, Windows XP, Windows Vista and Windows Server 2008 (http://support.microsoft.com/kb/971842)
You must have .NET Framework 3.5 Service Pack 1 (SP1) installed to apply this hotfix.
Note This fix applies only to Windows Vista and to Windows Server 2008. For a Windows 7 or Window Server 2008 R2 version of this hotfix, click the following article number to view the article in the Microsoft Knowledge Base:
981002 A hotfix rollup is available for Windows Communication Foundation in the .NET Framework 3.5 SP1 for Windows 7 and Windows Server 2008 R2
x64-based version of Windows Vista SP2 and Windows Server 2008 SP2