I have been noticing that alot of my B&W cause the Nikon Scan software to fail in the autofocus attempt during prescan. The Coolscan tells me the AF had failed and instructs me to remove the film by hand out of the carrier and try again. It seems to be hit or miss and I can't seem to pin point an cause. Color film seems to work fine. With B&W, I can prescan as positive or color mono in 8 or 14bit and I still get the same problem. Is this a workflow issue or something inherent with B&W film? Mainly Tri-X by the way. And what can I do to correct this?