How to set up a custom user defined paper size for your inkjet printer with Photoshop Elements Mac
For Red River Paper greeting cards, scrapbook 12x12 sheets, panorama printing, and other special projects, you need to define a custom paper size in the Page Setup dialog.
SPECIAL OSX ERROR FIXES
Apple OSX 10.6 and up has issues with handling custom sizes correctly. If your printer prints only a portion of the image, the image but in a smaller form, or will not print at all, you likely are seeing a custom paper size error.
Set paper width to 12.95"
This avoids problems with the 3800/3880 max print length of 37.5". You'll still have room for a full 12x36 or 5.5x36 print.
Margins must be set to 0.2" or larger. Smaller numbers may result in OSX designating your size as a roll and the printer will not print.