I had the same problem in Firefox, so the only thing I could do to resolve the problem was to clear my cookies. I don't completely understand why it is happening, and it is a very new problem for me, but once again, this did allow me to load and watch my video at Youtube after I cleared my cookies.

Updated post here, I find that if I turn my cookies off all together, then I can surf YouTube nonstop without having to clear my cookies constantly, but the downside is, I can't log into my account with the cookies turned off. Hope this helps all of you out there with this problem.