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In Prerelease section the status of your build should not be "Processing". Just wait some time (10-20 min) after build upload, and it will be ready to use.
I got this problem in Chrome browser. Switching to Safari worked like a charm for me.
I had the same issue. To solve it, the unique thing I had to do was "Clear History and Website Data..." within Safari (version 8.0.3 in my case).
Please, keep in mind that I speak from my experience and that worked for me. I cannot guarantee this as a general rule to fix the problem. Nevertheless I can assure that I tried several alternatives explained here and the one I just described was the solution for me.