When the EzeScan_Routing.exe runs as a service it can only access a mapped drive using a UNC path (i.e. \\myserver\volume1\scanner), not a mapped path (i.e. f:\scanner).
To correct this problem simply:
Stop the EzeScan_Routing service.
Start EzeScan.exe, Press F9 to go into the Routing Admin form. Go to the Import tab. In the Import Directory field change the mapped drive path to a UNC path by manually typing the new value into the field. Save the changes.
Start the EzeScan_Routing service.
Place some TIF files into the EzeScan Routing import directory. They should now be processed out of that directory.