Order import failure

I have an order import set of data from an external agency.  The data has been formatted correctly but many of the rows are failing.

The Tessitura report details the reason as "50000 Error occurred during import, check log.".  If I check the table T_IMPORT_SESSION_LOG the corresponding message is consistently "Duplicate: Potential duplicate for existing ID 61050360: Abbott, Penelope. Match using Name and Primary Address." - obviously with a change of customer_no, lname and fname as appropriate.  The report itself does not detail any potential duplicates so the only thing I can think of is that it is the potential duplicate that is causing the row to fail.

Can anyone offer any insight into what is happening here?

Martin