I developed two rolls of FP4+ in a Patterson tank today. The roll nearest the bottom of the tank turned out fine, the top one came out completely clear. The writing Ilford puts on the film was perfectly legible however. I checked the lenses, and they are fine - although I used more than one lens for each roll in any case and never really thought the lens(es) were the problem. This was my 77th and 78th rolls through a camera bought new by me, and it's never happened before. but I'm wondering if I could have made a mistake in loading the film? I'm not even sure it's possible to mis-load the film, but I'm clutching at straws here. I didn't notice anything unusual when advancing the film between shots. I'd be most grateful for any ideas. The film holder (same one for both rolls), camera and lenses seem to be functiong fine, and I'm sure the darkroom work wasn't at fault, so it must be something I've done.