Resolved: WCAT: Invalid code received - Run error detected, terminating clients

When implementing WCAT for load testing for the first time I ran into the overly vague error message below.

All clients connected, Test beginning.
 Invalid code received.
  message: Run error detected, terminating clients...
  message: Terminating all instances of wcclient...
  message: Terminating all local instances of wcctl.exe...

How to Turn On Debug Logging for Group Policy

When you are troubleshooting group policy issues, it's helpful to turn on some additional logging. Unfortunately, it's not just a simple switch you turn on. You have to know what you are doing to get those logs.