I am not familiar with Fathom and OpenEdge Dismanagement anymore - haven't done anything with in for ages ...
But, from my experience such an error comes from the WebServer responding to the browser's request but not sending any HTML code back in time.
The web server embedded should have a log file which should reveal more details on the problem. Only trouble is to find out where it is located.
Heavy Regards, RealHeavyDude.