This post is written as a result of attempting to run an existing EPiServer CMS 6 R2 solution on new build Windows 8 machine. If you are trying to use the EPiServer 6 installer to install a new site on Windows 8 take a look at Arild Henrichsen's blog on the EPiServer 6 Powershell bug on Windows 8. However if you are having trouble running an existing EPiServer CMS 6 R2 solution on Windows 8 read on... 

You may experience this bug if the following conditions are true:

  • The machine is a new Windows 8 build (not upgrade)
  • Running an existing EPiServer CMS 6 R2 build
  • Site has NOT been upgraded to .net 4.0


On starting your application you may get the following YSOD message "Could not load file or assembly 'System.IdentityModel.Selectors, Version=, Culture=neutral, PublicKeyToken=b77a5c561934e089' or one of its dependencies. The system cannot find the file specified.":

This is due to the fact Microsoft decided to miss out an assembly from version 3.0 of the .net framework on Windows 8.

How to resolve

Get a copy of System.IdentityModel.Selectors.dll from another machine. You can copy the file from the following location on an upgraded Windows 8 or any Windows 7 (Server 2008) machine. You need to ensure you run this at a command prompt not windows explorer / File manager:


Run the following command from an elevated Visual Studio command prompt in the same folder where you copied the file above (this will install the missing assembly in the GAC):

gacutil /i System.IdentityModel.Selectors.dll

There is also a hotfix from Microsoft on how to resolve this:


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