Is a document jammed inside the ScanSnap?
Remove the jammed document, and perform scanning again.
For details, refer to Removing a jammed document.
Is the ADF top section open?
Remove the document that you are scanning, and close the ADF top section .
If none of the above is applicable, close the ADF paper chute (cover) of the ScanSnap to turn it off, and open the ADF paper chute (cover) again to turn it on, and then perform scanning again.
Make sure that you leave at least 5 seconds between closing the ADF paper chute (cover) and opening it again.