Thanks for all the suggestions. Waiting on the phone while the senior support staffer looked up further info, I tried printing a different, slightly smaller 15 X 33 image on 17 X 35 paper, and it printed just fine. Checking further, I realized that the paper setting was 40 X 17 for the problem print, instead of 17 X 40. Changing the setting to 17 X 40 (for the 15 X 38 image) solved the problem. I'd never had problems with reversing the paper size numbers before; and in fact, the 40 X 17 did print out once, albeit with a 15 X 39 image instead of 15 X 38.
An interesting side note, the tech asked if my printer was close to a window. It seems that there are occasional problems with window light interfering with the printer functioning correctly.