brother mfc-8910dw "out of paper" error when printing from pdf

This is, let me start by saying, that this a fine printer that has worked for me for years.

Recently, however, it has been behaving strangely when printing pdfs either from adobe or within Firefox, for example.
There doesn't seem to be anything wrong with the printer since it prints PERFECTLY from within Word (from all trays) and scans from within Brother's own program or from within Abbyy finereader.

The error message I receive is "out of paper," which doesn't clear when I cancel the queue or reboot the computer and printer.
There is paper in all trays. Again, I can direct Word to print from any of the trays.

Flummoxed.

Thanks in advance for your help.

Richard

No, I already thought of that. Spend a lot of time in Paris where I use A4 and always check paper settings because I don't remember in what format I saved a document.
Good stab, though.
Thank you!!

Deleted driver.
reinstalled driver.
still no go.
went to icon of printer in devices and printers in control panel.
clicked on ethernet address to the right of the icon, which gave me a list of ports to which the printer can print.
found that the usb virtual printing port was unchecked.
checked it.
BINGO EVERTHING WORKS.
Thank you!!
what unchecked the printer port? no idea.
anybody want to guess?
probably happened with one of the windows 10 recent updates.
i got lucky.