Listing items can gets tricky sometimes. There are many different errors that pop-up when listing items.

At times there are many false positives as well.

These instructions are in the event that you're thorough everything is okay from your side and the error that is displayed on the screen is a false positive.

Resolution:

Click the options button for the item

From the drop down options, select Mark As Valid.

This will mark the item as valid.
Once the warning is removed, you can submit this item again.

If the item comes back with another error after marking valid, then there is another issue with it that will need to be corrected first.