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
Increasing Engineers on iOS 7 questions time left –
With the WWDC 2013 closing in, Apple have been reportedly borrowing engineers to finish iOS 7 in time. The new Operating System for iPhones, iPads and iPods is set to make a preview in San Francisco between June 10th to the 14th.
Sources report that company has been borrowing programmers from the OS X 10.9 team as part of an effort to speed up production time. This is most likely due to Ive’s new role in the interface design for the new OS. The new OS is set to have improved graphics and more gestures to enhance the merge of hardware and software. This was discussed last week when news came in about Ive’s “very, very flat” design which can be seen here. One source talks about the whole of Game Center will be refined design wise, removing all elements of the green colour scheme that have been evident since its release.
In simple terms, the iOS is like an old car, and iOS 7 is the same car but with a completely new body kit.
This complete design overhaul evidently is pushing on Apple’s time left and resources but this new design is much needed since the lack of change since the iPhone’s release in 2007.