Add STS Reference missing in Visual Studio 2010
If for some reason, you reset your designer settings or revert to an older version, you will notice that the add STS reference command is no longer available.
To resolve this, all you need to do is
1. Run Visual Studio Command Prompt in administrator mode
2. run the following command
“C:\Program Files (x86)\Microsoft Visual Studio 10.0\Common7\IDE\devenv” /ResetAddin Microsoft.IdentityModel.Tools.VS.VSAddin.FederationAddin