It looks (to me) like your computer is trying to make the secure-socket-layer (ssl) connection properly, and the website you are trying to connect to is having problems with ssl at their end.
because the authenticity of the received data could not be verified.
If it was an error on your end, this conclusion would have been different:
* Please contact the web site owners to inform them of this problem.
EDIT: Forgot my conclusion!
Many factors could cause this. Certain times of day? Because you are using Firefox on an MS Site? Just a busy time on their website? New cookie, script rules at their end? Script/cookie blocking on your end?