Constant "load paper in tray" error even when paper is loaded.

The switch inside that makesxeither an electrical connection orca mechanical one tells the printer that the paper tray is home loaded and awaiting commands is not being activated by the tray
The switch has become faulty overtime and needs,a replacement
The bit on the tray that pushes the tray loaded switch has broken off the tray is missing the switch or a wiring fault has developed
And the switch has no power so it still can't see the tray even if it is loaded thus error paper tray missing continuously is being displayed

The obvious thing is to turn the printer off, remove paper tray, take out the paper, look to see if anything clearly amiss with either the printer or the paper tray itself, reflll the paper tray with a moderate quantity of preferably fresh paper - though this should not matter - and replace the newly-loaded tray. Turn the printer back on and see if it works or not. You may also try single sheet manual feed if this available for your printer.
12.March.2015

You sent a paper size different of the requested by the printer. Just load the requested size or delete the spool.
Some PDF downloaded from internet has A4 or 8,5x11", maybe is requesting one of this sizes.

If you can not delete this message, delete the spool using the printer manual in the control panel of the printer.

There are two places to insert the clip on the right side of the paper tray. Replaced the clip into the top slot and the printer works fine again.

490 error means -

LOAD mmm AND PRESS ONLINE SWITCH 490: MP TRAY EMPTY

Print job from MP Tray has been received and the MP Tray is empty.

Load the requested media (mmm) in the MP Tray and press ON-LINE.

Check your print driver settings and see if your defualt try is set for the MP Tray. Also see if the page setup for the print job is set for MP tray.

Check the Paper Handling Menu. The Tray 1 size and Tray 1 Type should be set to Any Size. This means that the printer should pull the paper from Tray 1 first when paper is loaded in tray 1

I have a Dell 3010n myself, and a few times I did run into that "Load MPF" issue.
1.) Before printing a document, please check and see the properties. i.e. Kind/type of paper, which tray, or if printing envelopes or any other document than a regular 8 x11 paper. Putting all the tray and paper type selection on "Auto" can be very helpful.
2.) On the printer itself, there is a menu button where you can configure the type of paper, i.e. regular 20 llb. copy/print paper, glossy photopaper, thicker paper - after you place a fresh load on the paper tray and slide it in, usually it will ask you which type of paper you just loaded. Make sure it is the same settings as the document that you are trying to print: i.e. if document settings on computer was set to print on photopaper and you have regular paper on the tray, the printer will do a "Load MPF".
The paper sensor on it is amazingly (for a Dell, that is) sensitive and it can differentiate across a lot of paper types/thickness. If you have several computers and user across a network, and there are several paper-type settings done on the printer itself, this "Load MPF" issue will present itself more often.
In my case, it's simply because the person who recently changed the paper-type to glossy cover paper from some user who previously printed to a transparency forgot to revert MPF/Tray 1 to regular copy/print paper. Most cases, the printer setting on the PC has been left to print on to a transparency by default, so even if I stack the tray with copy paper to the hilt, it still will do "Load MPF".

Dell 3100cn Color Laser Printer Error 024-965 - Load Tray 1

Cause:
The "Paper Tray Inserted" sensor buttons are not being depressed by the Paper Tray so the Printer thinks no Tray is inserted even if the Tray is properly inserted.

If you pull out the paper tray and look at the Paper Tray opening, you will see three white vertical sensor buttons along the left-hand side at the mouth of the aperture where the paper tray slides in. These three white vertically aligned push button sensors tell the printer that the Paper Tray is inserted when the paper Tray is
properly pushed all the way in and aligned. It also signals to the printer by noting which button is depressed whether the tray is a Letter Size or Legal Size tray that has been inserted. These buttons which are fully visible as soon as the tray is slid out can move out of place and even fall into the wall of the Tray slot preventing the buttons from sensing the tray.

Solution:
Click it back into place. There should be no play and the buttons themselves should be the only thing that move and then only in an in and out manner. They should move out toward you when the Tray is removed and be pushed in when the tray in slid into the paper tray feedering slot. A pair of needle-nose pliers may be necessary to draw the button module out of the tray slot wall if it has fallen in. Once it is STIFFLY repositioned and the Paper Tray reinserted, reset the printer by opening and quickly reshutting the printer cartridge compartment. This action will recalibrate the printer, shut off the amber error light and resume the current printing job if one was in progress.

Good luck!

Check your printer for paper size and type settings. Ensure they are set to letter and plain1. Also check the program you are printing from (Word, wordperfect, etc) and ensure the paper size is correct there as well.

1-Is the paper set correctly in the tray? if you have Letter paper in it make sure the guides are snug against it

2-Check the lever inside the tray, remove the tray and look at the tires there should be a lever that you ca move freely that is the paper sensor