[Ifeffit] combining marked groups

Ifeffit Dudes, I've tried to plot several groups together in Athena and then saved them together under "Save Marked Groups---chi(k)." It seems to work fine, but then when I try to open it up in Artemis I can't do anything. If I try to graph something, it closes. I can't do a fit b/c there are no parameters. My question is this: how can I average and then fit several data files? Thanks, Dan