I am having exactly the same problem. If I try to install Unyte by going to Tools | Do More | get Extras and then click on the green button I get "Download failure, error 404" which means it can't find it. If I go to
https://extras.skype.com/907/view and try to install it from there I get "To use this extra you need to purchase a valid license. Please clik the Buy Now button to proceed". And what is more, if I DO click the Buy Now button I get taken to a web page that says "Sorry, but the payment system is unable to detect your Skype client. To continue with order please close this page and restart your Skype client, then try again."
Does anyone know what on earth is going on?
(PS I tried deleting my cookies as suggested but that made no difference whatsoever)