Will not print to tray two message tray one empty stops

SOURCE: Okidata 5100C error code 490:MP tray empty

http://www.fixyourownprinter.com/reference/errorcodes/okidata

SOURCE: Stopping Auto Tray Selection

If you use different print materials of the same size in the trays, each tray with a different print material should have a unique paper type setting to prevent the printer from linking the trays together and mistakenly printing on the wrong paper.

From the printer's operator panel, choose the paper menu, then paper type, then select the source (ie, tray) that you want to change.

For example, if you have plain paper in tray 1 and preprinted paper in tray 2 and both are set up where size = A4 and type = Plain paper then when Tray 1 runs out it will automatically feed from Tray 2. To prevent this from happening you should change Tray 2 type = Letterhead. In this way, the printer knows that the two media types aren't identical and won't pull from that tray unless you specifically tell it to.

SOURCE: "490: MP tray is empty" message when trying to print labels from Word 2003

The MP tray referred to is the Multi Purpose tray and is located at the front of the printer. To access it, you need to find the 2 indentations at the side of the front feed assembly and pull them towards you. this then gives access to the MP tray. Don't forget to press the blue button after loading the paper. Your user guide/manual will give clear instructions and pictures. It may also be called manual feed tray. Once loaded with the correct paper press the online button and printing will start.

SOURCE: Paper Empty in Custom Tray message

there's something wrong with the paper sensor

SOURCE: MP tray empty?

MP Tray = manual tray
Change properties from your driver (change the tray)