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
WWDC 2013 Tickets Available Now
Yesterday Apple announced their annual WorldWide Developer Conference (WWDC 2013) will be in San Francisco from June 10 through to June 14. Tickets for WWDC 2013 have just this second gone on sale for $1,599 USD via Apple’s website and if last year is to go by they will not last long.
At WWDC 2013 Apple is expected to talk about both the next generation Mac operating system (10.9) and also the next version of iOS (iOS 7).
Apple was kind enough this year to give developers an early warning as to when they will release the tickets in to the wild unlike 2012 when Apple released WWDC 2012 tickets at 5.30 a.m PDT.