Image assist woes

Working on a new image for a swath of pcs we're about to refresh. Created new image in hyper-v, downloaded driver packs, etc etc...saved the image, no issues.

booted to usb to test image... image assist loads, everything looks fine, except that once the WIM is selected, the OK button is greyed out and I cant select it. I've never seen this before...google is useless, scratching my head.

Any ideas?  Not sure what to try here.