You have probably found the culprit by now since this post dates! But I remember having had some issues when I began using the GS1, that was a long time ago. The GS1 camera feels a little fiddly, but it is stronger than you would think and I never had to send it out for a repair in the years I used it. But one thing that can happen when mounting the back, if one is not careful, and especially when switching backs in a hurry, is that one of the two bottom (or top?) hooks can stay out, while the other is hooked. This can go unnoticed until you forward the film with the camera. Then the small dented wheels are not synchronized and you get problems such as you describe. If this is what happened when you got the bad behaviour, you would have noticed that it was difficult to detach the back. I never used the grip but only the rotating handle, and I don't have the camera any more so I cannot provide a step by step, but there should be a way to fool the camera to check if the dented wheel is turning, maybe by mounting the back and leaving it open if that is possible. I think there needs to by a film in to drive the mechanism. Also, if you don't have a manual with the camera, find one and read how to load the film properly, for there is a special manipulation with the double exposure lever while advancing the film, if I remember right. Bottom line, if it doesn't work, don't throw the baby out but take time to go through all the procedures until you master it. Be gentle with the camera and it should serve you well. PG lenses are great optics.