John something just occurred to me that if you can look at the paper trays and see if you can adjust down to that size or maybe there is a by-pass tray that can adjust as well.
If at the printer you are able to input that size, C60 is limited to 4 x 5.5, then maybe it can or that code you getting could also mean that the part of the tray that would accomodate that size is not installed.
If you can upgrade I recommend the C60
I have a Nuvera 100EA and have run into this problem before although I can't tell you what the error code means.
I believe you can create any custom size but unless the MFD has the abilities to accomodate such a small size then the best it can do is print on the standard sizes suggested in the operators manual.
You maybe able to run multi-up but that just means you will have to cut the pieces out of the chosen stock.
Check the operators manual to see if a specific tray has an option to print that size, it may just be too small.
Also if printing from Word, Publisher Acrobat etc., something you can use if it comes to printing multiple-up is to chose the "multiple-up" tab located in the print menu.
Of course if you cannot trim or have a cutter you may print it and ask it be cut this may help if you have to use an outside vendor.
Does anyone know if the Phaser 6180 MFP can print on 3" x 5" index cards? The printer driver lets me create a custom size with those dimensions, but, when I try to print, I get the error message: "016-799"