Duplicate name-value combination in variation specifics: this error usually apears when listing a new product that varies on at least 2 attributes but only one of this attributes is mapped to a ebay value.
1. Go to the products page on the "Associations" tab.
2. See the value of the "Default Category".
3. Go to the ebay module.
4. Go to the "Categories and Pricings" tab.
5. Find the category of your product and see to what ebay category it is mapped to, and save that category name somewhere.
6. Click the "Item Specifics" tab on the same page.
7. Find the ebay category you saved at step 5 and update the mapping to reflect the product variation types(attributes) in your local category. (Click here to see how to map your attributes to ebay balues, starting with step 6 on that page).