Rats. I *thought* I had managed to solve this by editing the CustomMenu.ini file in the GameEx Config folder but unfortunately that reverted so it still seems to be that if an 'item' is chosen as MAME it behaves like a folder.
I'm a newbee and this was the easiest part to add to my homemade garage pinball machine.
Everything worked flawlessly. Thanks for a great piece of software.