there are different scenarios for this behaviour. Unless you name the exact message at the panel when you print it's guesswork....
- Try setting Tray1 Type to plain and Tray 1 Size to Any (not both to any!)
- Try a cold reset, turn off the device, turn it on and hold the green button until all 3 LED's are permanently lit, release the button "select language" should appear on the panel. Use the up or down button until you see "cold reset" on the panel, then hit the green button again. The printer will automatically restart.
- Try upgrading the firmware. Even if you have the latest firmware already, still do an "upgrade" by redownloading it to the device.
- if it keeps getting set back to papertype light, someone is messing with the device, probably when one re-fills paper the device offers to change the paper type and people think they have to press something instead of just leaving that message until it goes away. With later firmware you should be able to turn this behaviour off.
Cheers
Lex