Paper output tray is open but message says it is closed
I solved this problem by putting a shim between the door & switch lever.
The shim is just a piece of cardboard/plastic/whatever about the thickness of a credit card & about 1/4 inch wide.
At the lower right corner of the paper outlet is an opening about 1/4 inch square. On the right side deep in this opening is a lever (rather hard to see). When the door is opened it lifts the lever up (presumably telling the printer the door is open). I took a small screwdriver, inserted it into the left side of the opening, turned it counterclockwise until it caught the edge of the lever & lifted it up, inserted the shim below the lever, & withdrew the screwdriver. This solved the problem (it has only recurred once since the shim was put in).
If the shim falls out just reinsert it. Of course, if you ever want to close the door you need to remove the shim first.
on Dec 28, 2016