I had problems getting the P900 to recognize the "sled" that I was using for the plates. I took clay harmon's workshop on dpt and he showed us the use of a sled - using two pieces of 2X matte board with the top piece being a frame to hold the plate. I also used a small tab of two sided tape in the corners to keep the plate secured?in the sled.
?Here is what I did - the carrier I used was two layers of 2X matte board - with a total thickness of 1.5mm. I created a custom epson .emy file for my DTP set-up based on the epson matte board .emy file ( you will have to down load this from the epson site). I modified the thickness parameter to 1.5mm and set the platen gap to 2.1mm ( I believe these are the largest values allowed). I also changed the .icc profile to a matte paper profile to insure the use of MK ink. After I made these changes and installed the .emy file in my printer, I was able to successfully load and print several plates... but it can be kind of "finicky" - also make sure all of the parameters on the printer set-up match the information in the print tool or QTR settings. Good Luck" ?A measurement of the sled would be useful, there seems to be a somewhat wide range of thicknesses of 2x matte board.? Apparently there are other issues that can cause the media to not be recognized -including stray marks on the sled, I am not an expert on any of this, but this custom . emy worked for me. Not sure if this is the best solution to this issue but it has worked for me.?
