When ever I try to print on my Canon iP3000 I get this message - Document printing cannot be executed because the paper output tray is closed. Open the paper output tray. Printing will restart.

The blinking is just an attention light so there's nothing to worry about that. Try adjusting your paper tray to the paper size you are about to use. Or try checking the duplexer panif its positioned properly. Hope this helps.

If you can remove the tray - have a look at it and it should come out without much force by pressing on the sides. If it comes out you may see the sensor inside that maybe is bent up and is not registering that the tray is open. If you see it you can bend it back down. You can also shoot canned air(with the tray in the out position of removed from the machine) and a piece of debris may come out. Use short squirts or the can gets very cold. All the office supply places and computer stores sell the cans of compressed air.

If none of the above helps, you can always communicate directly with Cannon at:

http://usa.canon.com/cusa/office?pageKeyCode=contactUsLanding

I have found them to be very helpful. Good luck..............................Pete

there is a problem in the printer it is the carbon

The printer will not print as long as the paper output tray is closed.

1. Open the Paper Output Tray (2).
   Put your finger in the rounded indent beside the Paper Output Tray and open it gently.
   
   
2. Open the Output Tray Extension (3).
   Open up and set the Output Tray Extension completely by pressing down the hollow on its front side.
   
   
3. Adjust the position of the Paper Thickness Lever (4).
   Set it to the right when printing on envelopes or T-shirt transfers, and left when printing on any other type of paper.

Slap the printer with your right hand from the right side of the printer.This process always solves the problem. I did, it worked

Canon Pixma MX300

- new cartrige for Black ink
- can scan
- can photocopy documents
BUT can't print documents from my MacBook eventhough the paper feeds and goes out at the other side

Just fixed this problem on mine. Need to remove the covers, watch these 2 vids to see how..
http://www.youtube.com/profile?user=martop49#p/u/1/iQdHDR6po80

Then on the right side where the on switch is, near the hinge is a little switch with 2 yellow wires, it's probably broke. Pull the 2 wires out and solder or twist them together, then put everything back together. It will now assume the door is always open. Jobs a good'n :)

lift the tray a little...

there is button or clip backside of the printer.......u just press it and open the tray..........it is also possible that u don't attch ur usb wire to the cpu u just check it .........may be it will be good........

Apparently a solution has already been posted here: http://www.fixya.com/support/t345435-ip4300canon_printer

The author provides instructions on opening the printer and gluing the sensor into the "open" position (assuming that the sensor still works).