PLEASE look in the 'Flight Data Recorder'

If you want to help yourselves (and support, escalation into Dev) learn to check the Windows Application log and the Epicor App Server log in Windows Event Log Viewer when a user complains about an odd error (below). This is where we log all ‘non business validation errors’ (e.g. - it won’t log you forgot to fill in a field).
The error should contain a stack trace with as much detail as the dev put effort into so not perfect but extremely helpful to accelerate the triaging of what went wrong.
The Epicor App Server is where all framework issues are logged and if WCF / dotnet completely died then it falls back into the Windows Application Log.
More details and filters are available in all the appserver.config traces and profiles but those Windows Event log entries are a great place to start.