I have been scanning to .pdf on to a USB stick for about 6 months on my LaserJet Pro 400 - M475dw. Suddenly it is saying "Insert USB Flash drive" every time I try to scan, even though there is a flash drive already inserted.
I have tried all 3 USB sticks that I have previously used, plus a couple of others. I have also tried reformatting them. All to no avail.
Today I updated the firmware on the printer to see if that would help - but no. :(
Have tried turning it on and off, many times, including leaving it off for up to a few days.
Has anyone else had this? Have you managed to resolve it?