That helped but there still is a problem, maybe more than one.
After swapping out and uploading the new file, I was able to create a coupon and then go through the motions of adding the coupon to a specific product (that's the good news), but the coupon got applied to all products anyway (not so good).
That is, after adding a couple of products to the shopping cart, only one of which should receive the coupon discount, the discount was applied to both products after entering the coupon code. This is consistent with the coupon details page which says that "all" products are included, instead of the lone product I attempted to connect to the coupon.
Secondly, when I try to edit the coupon itself to make it product specific, I still get the original "No input file specified" message on a new page. So, this result is the same as before the file swap.
This feels like a bug, but maybe not if no one else is seeing this result. Any other ideas?