If you're getting a stock 500 error when attempting to run a legacy .NET application on a Windows Server 2012 instance on IIS 8.5, make sure your application pool ID is set up properly.
On IIS 8.5, the Application Pool Id is normally set to ApplicationPoolIdentity instead of NetworkService - here is how to change it:
Also, make sure that your Application Pool is referencing the .NET 2 framework and not the .NET 4 framework.;
Please consider what you post!
Chillax if you're angry.