If you are prompted with the Confirm Unsubscribe Link pop up every time you try to save your Campaign, the problem will be with the Template.
This error appears when the block containing the unsubscribe link has not been locked down. The good news is that this can be easily fixed by navigating to the Template, clicking the Drop Down Menu then selecting Edit.
Click the Settings cog above the block where your Unsubscribe link is located and tick the Locked box.
This option will lock down the Content block and stop the Confirm Unsubscribe Link from appearing when the Campaign is saved.