Fresh Install of Windows 7 Enterprise
Fresh Install of ScanSnap S510 Manager 4.2
Double Click "SsDrvRepair-x64"
in the x:\Program Files (x86)\PFU\ScanSnap\
Driver\SsDrvRepair Folder
Accept Warning about installing driver
ScanSnap now works
I believe all you need to do is run the "SsDrvRepair-x64" and that fixes everything.
Cheers