This happens when you try to add products in magento having duplicate names . If the magento had already a product with same name the url is generated according to the name . So in short DON'T DUPLICATE PRODUCT NAME if you are not specifying product urls manually in the upload csv
There are 2 possible solutions .
- change your product name in the rows 4, 5, 6 manually in the csv and you will be able to upload the product. after that you can open the product from the admin and change it back to whatever you want
OR
- Add a new column named url in the csv and specify a unique url in the csv for all product. This way there wont be duplicate urls even if product name are same .