OK,
I opened the Scenario editor from the Matrix splash menu.
Selected EC2003 Battle for the IOPG.
Selected the first scenario, "Wrath".
Changed the game limit from 1 day to 2 days. (Game time to go in the editor shows 2:00:00:00).
File > save scenario as > created a new folder within Matrix>HUCE and saved edited scenario as Wrath_edit.scp
Open HUCE from the Matrix splash menu, load user scenario, navigate to new folder - nothing shows up.
Use Windows to navigate to the correct folder, there are two files present: Wrath_edit.txt and Wrath_edit.scp.
It looks like the sim is looking for a *.hp? file...
Completely unrelated, how do I get HUCE to stop launching a random scenario each time I open it?