What is the primary key on table MVF_Transport_Acc?

Try running this

CREATE TABLE #FileData
(
  RowNo   INT   IDENTITY(1, 1) PRIMARY KEY NOT NULL
, FileRowID CHAR(2)  NOT NULL
, FileRowData VARCHAR(20) NULL
, GroupID  INT   NULL
);

You need to use a technique which maintains the physical order of the rows in the file in order to be able to add any sort of grouping identifier.
The...

Is there a backup running at that time?