So, I felt like trying something "stupid". The file is definitely an xls (1997-2003) file, however, I set the import wizard to xlsx (2007-2010). Worked straight away.

I assume...

Oh a 4 day Scenario. Give this a go instead:
WITH RNs AS(
  SELECT *, ROW_NUMBER() OVER (PARTITION BY FieldSort1, StartDate ORDER BY FieldSort1, FieldSort2, FieldSort3) AS...

This is so much a SQL question, but more C#, so I'm not sure how much of a useful response you'll get here (as a SQL Server forum).

If,...

That doesn't really help clarify a lot here. Could you post the VB Script? Please ensure your encapsulate it in IF Markup so that it is easily readable. How are...

Why not create your Backup on a different location to your server and restore from there instead? A separate SAN, a Network location, or even an External (USB) Drive would...

What are the error messages in the SQL Server's logs? When using sqlcmd and SSMS are you using the same credentials? Same User? Both Integrated Security/SQL Login? It might be...

As pietlinden suggested, you should really rad the topic on how to post T-SQL questions on this forum. It makes things a lot easier for us, as we don't need...