What you need to do is look in the area where your copied pages come out, Between the paper tray and the bottom of the scanner.
On the underside of the scanner you will see a green latch, It is the only green item on the underside of the scanner. About 2 inches long and a half inch wide.
Turn off the machine, push that lever in, then, and it may resist some, pull it toward yourself until it snaps fully to the front of the machine.
My WC 3220 is showing "scanner locked" on the display. This appeared after I removed the ADF to replace a hinge. Removing the ADF required that I disconnect it from the base. I've confirmed that upon replacement of the hinge, the connection is secure.
The maintenace manual simply says to unlock the scanner. The problem is that I don't believe this unit has a switch to unlock the scanner.