I've been following this thread as it has progressed, but now I have a question. Perhaps I've missed something along the way but I just scanned all posts again and cannot seem to find anything referring to how you have been loading the paper. Due to the size of the image I'm wondering what size paper you were trying to print on. I can only surmise that perhaps you were cutting sheets from a roll and they were not a sheet size that Epson uses for the P800. If indeed you were actually cutting from a roll, you should have cut to a standard size and then it would probably have worked. Now that you have the roll adapter you can use the roll paper as it is meant to be used.
Just a thought
You are quite correct that I was cutting the paper from a roll. I had hoped to avoid the cost of the roll paper adapter as I don't do a high volume of printing and found the cost of the adapter to be more than I wanted to spend. I was able to feed the cut sheets both through the sheet feeder and the rear feeder but encountered the problems I described. I wasn't cutting the paper to a standard size as I had bought the roll paper specifically to be able to print photos that were greater than 22" in length. I don't really understand why almost all sheet papers are sold only in 22" lengths for 17" wide printers. This is a size that seems to me to be based on a doubling of the standard letter paper, which isn't sized for any photographic purpose. A standard 35mm image at 16.5" wide would print to 24.25" long, which would need a 25" paper length. And any panoramic images require greater length. It further confuses me because when I was using a 13" wide printer the standard sheet paper size was 13 x 19, which accords well with the printing of 35mm images.
I had expected that cutting paper from the roll to the size I needed would work as I had read about other people doing the same and had done the same with my Epson 2200 printer. I thought that as long as I gave the printer the sizing information for the paper all would be well. You seem to be suggesting, and my recent experience tends to support, that with the P800, at least, paper sizes other than standard ones can only be used with roll media. All is working well now with the roll feed adapter and I am now hopeful that was the answer to my problem.
Mark Haffey