After creating the schemedef and starting Programmers Notepad 2.4 RC portable I can select the scheme and also see the keywords in the “Fonts and Colours/Advanced” options.
So I think the schemedef file has been read in correctly.
But when entering a keyword in the editor it remains black. I had the same problem when updating from Programmers Notpad from 2.2 to 2.3 with a different schemedef.
Is there a way to delete the compiled scheme like in the not portable version (.cscheme)?