I don't know.
I had a customer call this exact problem in.
We had an analyst configure the machine initially and so he could have used a clone "hiding" aka unregistering the app from the home screen.
Print from usb was enabled but without the 'print from' app showing on the tablet's home screen there wasn't a pop up option when someone stuck in their thumb drive.
We have the C8030 and I have updated all the settings to allow print form USB but the problem is that when a USB is inserted into the port nothing happens. The device is not detected and I receive no error. The flash drive is formated to FAT, which I believe is a requirement.
The security is set to enable all ports and enable print from USB.
Ive no idea what to try from here.