Found out what was going on. In my first try to run a game with the Apple 2gs driver, I used the flop1 paramter (which expects an 5.25" disl) and also used an -inipath parameter. This changed the floppydisk1 line in the ini file, but never cleared it, even when I subsequently used the -flop3 parameter, so the first disk it encounters were effectively in the wrong format. when I omitted the -inipath, it worked. Here is an excerpt from the ini file:
# IMAGE DEVICES
As soon as I cleared the floppydisk1 parameter, everything worked as expected, even with the -inipath parameter present.
Thanks for your help.