Hello,
Usually, delete fail when element (folder, template, etc.) is still use somewhere.
Like an emailing, your website,....
About the message, I guess you're trying to delete a folder (it's not an offer) => it's a level more important than an Offer and should have important impacts.
Anyway, you should set 0 priority on the offer.
If deletion is impossible, the offer will never appear.
Best regards