This article explains why you are receiving duplicate lines of products when you process EDI 810.
If you process an EDI 810 Invoice transaction and find that there are duplicate lines of products, i.e. you see line 2 on the transaction file twice, then you most likely have more than one Customer Product ID for the Acctivate Product ID on that line of the invoice. You should see a different value in space 4 of the 'I' line on the 810 for each duplicated line. That is the Customer Product ID field.
Acctivate doesn't block you from having more than one Customer Product ID per Acctivate Product ID. When you process an EDI 810 Invoice, though, it doesn't know which to use so it adds both to the transaction file.
To find the Customer Product ID for a particular product you can go to the Product Information window and select the Search tool. In the field search window (top left corner) choose Customer Product ID. Then you'll be able to enter the Acctivate Product ID for the Product you have two lines for on the invoice. Then you'll need to go to the Customer record used on the invoice and go to the Product ID's tab and scroll through the list until you find the Customer Product ID that is duplicated or entered incorrectly. That is where you'll be able to edit or remove the duplicate Customer Product ID.