404 error after "connecting" site to concrete

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Hi,

We are having a very strange issue, completed installation of concrete which is all fine, then when i click the extend concrete theme, it then asks me to login which we then do correctly, then it returns a 404 error, instantly after logging into concrete, then if i try going back to either the add-on or extend theme page, it just says "your site is already connected"
I 've tried removing the values in Config table then clearing cache, but i think it must be todo with the 404 error that i get straight after the login, this is the link that returns a 404:

http://www.concrete5.org/marketplace/connect/-/?ts=1353490292&c...

Any ideas please? i'm completed out of ideas! really stuck and want to use the purchase themes we have :)