I can't get the film to advance to the next frame with my HC401 135 film back. I picked up the 135 film back for my Pro TL some time ago and finally decided to try it out. I think I loaded the film correctly, although I wasn't sure how far to advance it since there is no "start" mark on 35mm film. When I attached the back and turned on the camera it sounded like it was advancing properly to the first frame and the frame counter read "1". I adjusted the ISO to 400 on the back. I put on a 45mm lens and went outside. The first frame seemed to take just fine but I noticed that the film didn't advance after taking the shot. (I'm using the Power Drive Grip WG401) When I try to take a second shot it won't release the shutter. I removed the grip and tried it with the crank but it feels locked and won't advance. I even tried it with the smaller power drive grip WG402 and no luck. I also double checked to make sure the camera wasn't set on multiple exposure. I'm not sure if I loaded the film wrong or what... Any advice?