A friend of mine was printing on an Epson Stylus Pro 3800, and as the paper tried to load the printer displayed an “Incorrect paper size” error even though the size of the photo paper matched the Paper Size selected in Page Setup. And it worked just a few minutes earlier.

My friend was trying to print multiple images on a sheet, in multiple passes. As a troubleshooting step, I turned the paper around and inserted it the other way. It worked. Why would the printer accept the paper size one way but not the other?

I came up with a theory about it. Unlike my older Epson, the 3800 can perform automatic nozzle checks and head alignments, and can sense paper sizes. I have read that it can do all this because of an optical sensor built into the printer. Now, my friend was printing images with large areas of black near the edge, and she was printing borderless. I believe that when she loaded paper that had a large black area extending about halfway across the paper, the optical sensor saw all that black and decided that the paper’s edge didn’t actually begin until the white area appeared.

I have also run into a similar problem where the Epson 3800 will simply say “Paper error” and tells you to press the paper feed button and try again. In this case I am feeding an edge that is partially printed along the leading edge, though not completely black and with a thin empty border along the edge. Even then, the 3800 senses a misfeed even though there’s nothing physically wrong with the sheet. Inserting a blank sheet loads successfully.

This behavior indicates that the optical sensor is designed to think of paper as a broad expanse of empty white, and it may incorrectly believe that long dark areas are not paper and indicate a paper feed misalignment. If you’ve previously experimented with multiple-pass printing on another Epson printer model, you may not be able to make it work on Epson printers that try to sense blank sheets optically.

Some reading on the Web indicates that certain Epson models are able to turn off this automatic page size sensing, but that feature doesn’t seem to be available on the 3800.