All your headers are returning 200 which means that your server isn't blocking the request. Chances are that your server is filtering the request or your browser is doing that. I've tested a few banners and works for me on the demo.
The only thing left is to tell us which is the banner that doesn't get saved and please confirm that is not saved and not that is not being displayed. Please don't mix concepts.
Unfortunately, this ticket has more than seven days without a reply or feedback from the original poster. We will now consider this ticket abandoned and its now closed.
Don't hesitate to create a new ticket if this matter is still causing you issues.