Follow the steps below to unlock the scanning unit or to manage error messages related to the lock switch.
Unlock the scanning unit
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The scanner lock switch is located on the bottom of the scanner.
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To unlock the scanning unit, move the lock switch towards the unlock mark. 
To be sure the scanner is successfully unlocked, move the lock switch back and forth, then leave it in the unlocked position.
Resolve scanner lock switch errors
If you get an error telling you to unlock the lock switch and you're sure it's already in the unlocked position, try the following:
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Try a different USB port.
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Connect the USB cable directly to a USB port on the computer (not through a USB Hub or other device).
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Try a different USB cable (if possible).
Always lock the scanner when you carry or transport it.