Ok, then that won't help you if you only use one tray. For this one you may need more support. Please call 1-800-821-2797.
I am not sure if you have tried this yet, but you can try turning on Auto Tray Switching to see if that helps.
This one is becoming annoying, our Xerox C405 is set to print on A4 when the specified paper is unavailible as per the screen snip. However it is still prompting on the printer screen and you have to manually tell it print on A4 in Tray 1, instead of it just printing