Fujitsu ScanSnap S1500M Operator's Manual page 230

3.
Select an item other than [Check Length] in [Multifeed Detection].
If you scan documents of different widths or lengths in one batch with [Check Length]
selected, documents will be detected as multifeeds and scanning cannot be performed.
Note that scanning Letter and A4 size documents in the same batch does not result in
multifeed detection.
4.
Click the [OK] button to close the ScanSnap setup dialog box.
5.
Load documents in the ScanSnap.
1. Align the edges of the documents.
2. Place the documents at the center of the ADF paper chute (cover).
Using the ScanSnap in Various Ways (for Windows Users)
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