Compilation Error in Prod Env

Question

I am running my App in Prod Environment. It runs just fine in DEV Env. But in Prod ENV we get the following error:-

Exception information: 
    Exception type: HttpCompileException 
    Exception message: D:\JLLAPPS\WEBAPPS\dealioprod\global.asax(86): error BC30002: Type 'SessionSecurityTokenReceivedEventArgs' is not defined.
   at System.Web.Compilation.AssemblyBuilder.Compile()
   at System.Web.Compilation.BuildProvidersCompiler.PerformBuild()
   at System.Web.Compilation.ApplicationBuildProvider.GetGlobalAsaxBuildResult(Boolean isPrecompiledApp)
   at System.Web.Compilation.BuildManager.CompileGlobalAsax()
   at System.Web.Compilation.BuildManager.EnsureTopLevelFilesCompiled()
   at System.Web.Compilation.BuildManager.CallAppInitializeMethod()
   at System.Web.Hosting.HostingEnvironment.Initialize(ApplicationManager appManager, IApplicationHost appHost, IConfigMapPathFactory configMapPathFactory, HostingEnvironmentParameters hostingParameters, PolicyLevel policyLevel, Exception appDomainCreationException)

It says SessionSecurityTokenReceivedEventArgs is not defined. However we verified that Microsoft.IdentityModel is present in the Lib folder. Any ideas or suggestions what to look for ??