It makes sense to me that the camera may not display anything it did not take. JPG is not JPG is not JPG is not JPG, to paraphrase Gertrude Stein. Without the original EXIF information, and knowing the image does not come from the camera, I can imagine Minolta programmers decided that ... "Is it a virus?" ... then don't display it unless the file clearly states (a) it's from THIS Minolta camera and (b) it has not been altered from it's original sate.
The file is there, and your PC doesn't care about it's origin, I imagine Costco will also not care, and will see it okay. But, only Costco can tell you if they can read the resulting Adobe JPG file. Why not save it as TIF and keep as much of the original information as possible? Resaving a JPG as a JPG looses more and more information each time. If the camera can't read it anyway, I'd use TIF, and explore what Costco can read. TIF holds more of the original information than does a resaved JPG.
Good luck, and tell us more - keep us informed.
Click!
Love and hugs,
Peter Blaise Monahon
Minolta Vivitar Tamron Fujifilm Ilford Kodak Adobe Hewlett Packard et cetera Photographer
peterblaise@yahoo.com