did you find a solution to the iCloud beta 4 problem you were having? I have the same issue. I have a dev account and have been able to sign into iCloud on the icloud.com site, my iPhone and on my mac but not on my boot camp partition.
http://forums.tipb.com/icloud-forum/217341-problem-icloud-windows.html
http://forums.tipb.com/icloud-forum/217341-problem-icloud-windows.html
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