All the same chems were used for subsequesnt APX400 roll and that was perfect. I have never used and E6 chems or reversal kits for B&W so no possibility of this sort of contamination. There are also some strage marks along the film edges in places which look almost look like in places teh base has cleared largely, but there is a sort of tidal mark nature to them (wavy and not with clearly defined edges) Light exposure cannot be ruled out, but It cannot be teh camera (other rolls fine) . Also as I used a motordrive at points, one would expect some to be less fogged than the oned sitting ready to be exposed in the camera between frames. This is not so. Changing bag is always double checked, proocessing tank likewise. If there has been some form of fogging, it looks too even. Film canister leak? To me it looks intrinsic to the film makeup. If it had fogged it would have looked like any fogged frame (darkslide removed off camer etc). This does not look like this. As I say, teh undeveloped leader from the same film does not clear either. I bet something strange happed during manufacture...This is unlike something I have ever seen...the base still has a that sort of unprocessed look to it...I may even try to print one, though the exposure would probably be a minute or two....