You export your products and you get an error message like this one:
Duplicate reference...
Each concerned product is a duplicate, that means that the product reference is present at least twice in the database which is wrong.
Example for duplicate:
You must ensure that each product and each combination has a unique reference as shown on the page: validate your catalog structure.
You can then find a product displayed in this list of identifiers, thanks to its Product ID by searching in your catalog, for example:
