Uniqueness error - there is already an item with that name or name/parent combination

I'm trying to update inventory items in netsuite, the initial upload went well no problems. And the first few tests of the update process went well. However I have started to get this error:

Uniqueness error - there is already an item with that name or name/parent combination.

I am using the .NET package my pseudo process is as follows:

Ingest update File
Search inventory items for an existing inventory item with the same UPC
              if inventory item found:
                return the inventory item object
                set item properties using the values from the update file
                use the .update() method to update the inventory item record