If you encounter an error referring to "File Volumes are not sequential" when loading AddressBase data using LoctatorHub there is a good chance it is due to a known problem with the data supplied by the Ordnance Survey.
The Ordnance Survey have recently identified an issue which affects some AddressBase Premium data that they supply in CSV format. The problem is with the volume numbers that are contained inside the headers and footers of the csv files.
Details of the issue, and how to resolve it, are documented in the Release Notes for the May Release of the data (Epoch 15).
The Ordnance Survey have now released Epoch 16 of the AddressBase data.
They have confirmed that the issue has been resolved in this release.