I was having a terrible time using roll paper, and it turned out to be two mechanical problems:
(1) a white roller down inside the printer that was stuck down, due to a burr or some other snag, which a technician corrected by sticking a screwdriver down the back paper feed slot and pressing the side of the roller. It popped up, and he thought the problem was solved, since he had seen this before, and hadn't been called back.
Solving Problem 1 worked OK for the Canon Matte Coated paper and the Fine Art Bright White (after a struggle), but I couldn't get Canon Waterproof Canvas to load AT ALL. I tried to feed it in as far as it would go, but the paper wouldn't move or go into its back-and-forth roll paper load routine. Then the roll feeder would retract the paper completely and the printer had the audacity to say "Can't detect papr" [sic]. I called back the service technician, and he came out again. He determined that:
(2) the forward feed mechanism on the auto roll feeder wasn't working. The paper would retract, but not advance the paper. He took the auto roll feeder off, and we could hear something sliding around inside. I suggested perhaps a screw loose; he said it sounded more like a spring. He took it apart, and sure enough, it was a spring that was supposed to keep a gear in place that had come loose. He put the spring back in place, and it seems to be working fine so far.
All this was very frustrating, since I had already printed 20 or 30 feet on Canon Matte Coated roll paper without any problem. Then one morning I sent a print job and got the "Paper jam" message, then the "Can't detect papr" message when I tried to reload the paper. As soon as I inserted paper, the feed rollers on the auto roll feeder would clamp down and not move.
If it's working properly, you only have to feed the paper in just enough for the roll feeder rollers to grab it and the printer should take it from there. According to the technician, there is a slight curve in the paper path which might cause a problem if the roll paper has too much curl near the end of the roll.
I asked the technician about what happens if the leading edge of the roll paper isn't exactly square and he said the printer doesn't care too much about the leading edge -- that when it's checking paper alignment to prevent possible paper jams, it's checking the side edges of the paper.
I also asked him exactly which area inside is the platen, which you are supposed to clean periodically. (The illustration in the manual is somewhat vague.) It's the 1-inch strip of plastic with all the little vacuum holes and several slots with beveled edges to catch the ink and drain it into the maintenance cartridge when you print borderless. It's those beveled slots that you clean. He showed me there was ink on them even though I haven't printed any borderless prints yet -- the printer spits ink into these areas during a maintenance cycle or startup cycle. Interesting.
Another tidbit: the reason the print heads stop moving if you open the cover while you're printing (unlike my Epson 2200) is because of an OSHA requirement. The mechanism is strong enough that it could really cause serious injury if you were to stick your finger in there while the print heads are in motion.
I hope this helps in diagnosing your problems. In my case, at least, it was not a firmware issue, an operating system issue, or anything relating to sleep mode.