Sometimes, for absolutely no good reason, a printout will try to print itself out at the manual feed tray. It refers to this as "MBF" and will give the message "Load MBF....blah blah" On occasion, the message will take the form of "Load Legal Size...blah blah"
There is a very simple fix to this.
Whenever the printer is tied up at that message, just hit the number 3 on the printer's control panel (number keypad). This will make the LCD screen show "Print using Letter Plain" or something similar to that. Then press the number 4 (also known as Enter) and the printout will immediately come out.