HP Photosmart C8100 All-in-One won't print (Printer says "out of paper" but need to pull back the blue photo tray).
You RTFM. No help.
You go online to HP's troubleshooting guide for this exact problem and they have a detailed list of things to try except none of them fix the problem.
I figured this one out myself but if you look here somebody else did too
Another possible issue not identified in the video:
these printers are equipped with a blue “photo tray” in the main paper tray area. If this is pushed in, it’ll try to draw from that instead of the main train tray, causing this same type of error. The solution is to reach your head in, and pull out that blue tray until it is flush with the main tray.
Yeah, you need to pull that little blue photo tray back a few inches and - voila - the printer prints again. (I don't think yoofah meant to reach your head in - I think he/she meant reach your hand in - but then again, I had to do a little bit of both to figure it out myself.)
The problem here is that this 10 second fix for a problem that renders the printer non-operable is never mentioned in the manual (so RTFM does no good), not mentioned in the error message, and not mentioned in HP's online troubleshooting guide.
I post this here - hopefully someone may find it useful.