Same problem but just bought Cookie 5, it was working fine (I'm a longterm Cookie 4 user, rather annoyed I had to upgrade since the Safari cookies just stopped working) I got the update alert, I updated to 5.8.1 and now I get:
"“Cookie 5” is damaged and can’t be opened. Delete “Cookie 5” and download it again from the App Store."
Tried that, it doesn't fix it. Thinking I should ask for a refund from Apple...this is ridiculous.