EBay makes slight changes in the structure of return shipping policy from time to time and if it has been a while since you last updated it in eBay you might get the "Return Shipping Policy attribute not valid" in the lister.
The solution for this is as following:
Open your return shipping policy in ebay and SAVE, or even better create a new return policy and transfer all your listings to it, delete the old one in eBay (cleanup button in eBay policies section).
Come back to the monitor SETTINGS > BUSINESS PROFILES, first click "CLEAR FROM YABALLE" there, then "UPDATE FROM EBAY", then choose your default policies for Yaballe and SAVE. Wait till it's saved successfully.
Try to list something you hadn't tried to list before (not from draft).
Please contact us, if you need further help :-)