Is the glass of the ScanSnap dirty?
Clean the glass of the ScanSnap.
For details about how to perform cleaning, refer to ScanSnap Help.
An error may have occurred in the ScanSnap
Reset the ScanSnap by pressing the [Scan/Stop] button on the ScanSnap and the WPS button at the back of the ScanSnap at the same time for more than 5 seconds, and then check if the problem is solved.