you should reboot the settings and try again, hope it will work for you.
I'd also like to add that the usb port is enabled in the printer settings.
I'm having an issue with my Workcentre 5335 and printing from a usb stick. When I plug the stick in, the options to print from stick or scan to stick pop up so I feel it's safe to assume that the usb drive is detected - however, upon reading the stick for the files, I am then prompted to plug in "storage media container" and try again. I believed the problem might be the format of the stick so I've tried both exFat and MS-DOS (fat32) and neither have yielded different results. Is there something I'm missing/doing wrong? Thanks in advance!