Clearing cookies in logout

[kh99]

It oesn't look like there should have been any output before the logout_process hook, unless it's a php error message or warning. Have you used the browser developers tools to look at what cookies are being sent with requests?

By the way, you shouldn't use return from a plugin. If there are any other plugins using that same hook, it could stop them from running (but I have no reason to think that's what's causing your current problem).