Epson P800- paper source error- mystery roll detected

[marlakart]

I am trying to print cards through the sheet feeder.  I do this all the time.  Today, however, I am being told that "A roll paper is loaded, but the paper source selected in the printer driver is not appropriate."  I have never had a roll loaded.  I don't even own roll paper. 

I have already matched the paper source setting on the printer and computer.  I am at a standstill.  Help!

[Lewando_Images]

try turning everything off. Unplug the printer, reboot the computer and start over. This fixes lots of problems for me...

[MichaelKoerner]

Changed to roll in driver's paper source options accidentally?
Rear support opened accidentally?
Media slipped into the roll paper feed slot accidentally?

To be more specific:
Win or Mac?
Where are you told that - on the printer display or on your computer? And when - after hitting "print" button or before?