The Validation Server service will not start. 

The  Validation Server log file size grew to <4GB and the application is no longer able to read/write to that file. 

Check the validation server log file size. If it is <4gb, stop the validation service from the console and move the log file to another location. Don't leave rename the file and leave it in the same folder - it will not auto-delete during log rotation. 

Set the logging level to INFO and save the settings. 

Restart the Validation Server from the console.