What does this error mean?
This is a direct message from eBay for variation listings. It means the main listing and the variations use the same Item Specific.
How do I fix this error?
You'll need to
find which Item Specific appears in Product Details and the variations.
Then remove the Item Specific from Product Details.
For example, the Item Specific "Color" is used for variation specifics:
To fix the error, navigate to the Product Details tab, then remove the value for "Color." This will detach the Item Specific from the Parent.