My store has been up for a couple of months with no problems and taking orders etc.

I've installed Google Base, News box manager recently and that went well. I've just been testing my store and tried to buy a test product but get this message when I try and checkout:

Redirect Loop

Redirection limit for this URL exceeded. Unable to load the requested page. This may be caused by cookies that are blocked.

The browser has stopped trying to retrieve the requested item. The site is redirecting the request in a way that will never complete.
* Have you disabled or blocked cookies required by this site?
* NOTE: If accepting the site's cookies does not resolve the problem, it is probably a server configuration issue and not your computer.

What does it mean, what do I need to do to correct it???
It's not a cookie issue I don't think as I've not changed anything regarding that.

Please help anyone!!