Unable to list item. Product details cannot be edited because this listing has pending offers. Only price and quantity were successfully submitted to eBay.

Basically this means someone has bid on your item already or has made an offer to buy it. In cases such as this no changes can be made to item details other than price or quantity.
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This one is a hard stop and there isn't anything you can do about it besides ending the listing outright and relisting it with the changes you wanted to make.