Someone pointed me to what looks like the correct location

Run the Sage HRMS - System Maintenance program and you will find a 'Server Errors' tab.

That had the error I was looking for.

@Dave Boggess, you will need to access system maintenance on the ESS Web server. 

On the ESS web server, click Start, Programs, Employee Self Service, and System Maintenance.  Click on the Server Errors tab. Scroll to the bottom of list to see the most recent error log.