Dirt and dust may accumulate on the ultrasonic sensors (areas circled in red in the photo). Gently wipe the sensors with a cotton swab. For detailed cleaning instructions, see this page.
If the Problem Still Persists
Repairs may be required.
In that case, contact a local subsidiary near you.
Reference Information
If you set [Multifeed Detection] to [None] when only one document is loaded, the "Overlapping of documents detected" error message will not appear.
To change this setting in ScanSnap Home, open the [Edit profiles] window, click [Option] for [Feed], and set [Multifeed Detection] to [None].