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
OS X Mountain Lion Sky Rockets To #1 Paid App
We would not expect anything other then Mac OS X Mountain Lion taking the #1 spot at the top of the Paid apps chart in the Mac App store after it was released to the public earlier today. The future is looking good for OS X Mountain Lion as up to now in its short life it has received 80% 5 star reviews and 20% 4 star reviews.
You can download Mac OS X Mountain Lion for your self HERE
OS X Mountain Lion