SharePoint : System.InvalidOperationException: The farm is unavailable.

Scenario:

You receive the below exception when you try to access Central Admin / any SharePoint site.

Explanation:

Event ID from Event Log - 3


System.ServiceModel.ServiceActivationException: The service '/SecurityTokenServiceApplication/securitytoken.svc' cannot be activated due to an exception during compilation.  The exception message is: Exception has been thrown by the target of an invocation.. ---> System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.InvalidOperationException: The farm is unavailable.

   at Microsoft.SharePoint.Administration.Claims.SPSecurityTokenServiceManager.get_Local()

   at Microsoft.SharePoint.IdentityModel.SPSecurityTokenServiceConfiguration..ctor()

Resolution:

• Open IIS
• Go to Application Pools
• Find the security token application pool and click on "Advanced Settings"
• If you notice that the value for “enable 32-bit applications” was set to true, change this to false