I print from Photoshop, so maybe this won't help, but it could be the same issue. Earlier this year I posted this thread:
https://forum.luminous-landscape.com/index.php?topic=133606.msg1147828#msg1147828 all about my problem not being able to print a custom size on roll paper, and, if you go to the last post, you'll find my solution, which was think like a coder and be very exact in the language and labelling you use for your custom size.
"Yes! I got it! I was thinking in the gym, maybe this is a language problem. Maybe, yeah, I'm being too cavalier in naming my custom template "roll" (duh). Maybe it needs a much more serious label, like one of the above mentioned preset templates in the various sizes. So, I changed the name of my 17x44 custom size to "17 x 44 in (Roll Paper)", thinking like a coder, making sure the spacing and caps were exactly the same as "17 x 22 in (Roll Paper)" which is a preset, and, as I said above, actually made the printer print. Ouila! My printer started up, and I now have a 17x44 print of an image that, quite frankly, shouldn't be so big. Maybe I'll drop this size down a notch or two. But, success! Thanks for witnessing my agony."