In ProStores there are separate numbers for orders, invoices, and for tracking. This can be very confusing and our warning messages can be a little misleading. In the latest version of ProStores, the number reported when deleting a product attribute is the invoice number. This invoice can be located by browsing to the Store Administration and clicking on Order on the left. Then you will want to enter the invoice number and click the arrow.

Unfortunately, in older versions of ProStores the number reported was the actual order number and not the invoice number. To find the corresponding invoice number you will need to go to the Support Manager and export the Orders table. You can also go to the Report Manager, click on Sales, choose the Order Log report, and export the report to .csv format. In there you can search for the product by name or by SKU to determine which invoice has the attribute.