Edit: After half day, my wife’s Mac started having the same problem. I have then applied the solution that I found in the Apple
Apple Said To Post Session Video's During WWDC 2013
As you are most likely aware by now Apple just announced WWDC 2013 and said that tickets will go on sale tomorrow at 10am PDT. Apple also announced that they will be posting session videos during WWDC 2013, typically Apple would guarantee to post session videos weeks if not months after the conference.
Can’t make it to WWDC? We’ll be posting videos of all our sessions during the conference, so Registered Apple Developers can take advantage of great WWDC content.
This seems like the next best thing as most developers will not be quick enough to get their hands on some WWDC 2013 tickets.