Are you using an application/tool that communicates with CRM 2011 and facing the error?
CRM 2011 Error: Could not load file or assembly ‘Microsoft.IdentityModel, Version=188.8.131.52, Culture=neutral, PublicKeyToken=31bf3856ad364e35’ or one of its dependencies. The system cannot find the file specified.
Then probably you would want to install Windows Identity Foundation. The Windows Identity Foundation helps simplify user access for developers by externalizing user access from applications via claims and reducing development effort with pre-built security logic and integrated .NET tools. Download it from here and install.
Happy to help!