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 Issues OS X Server Codes To Mountain Lion Customers
Yesterday after Apple released Mac OS X Mountain Lion they launched the OS X Mountain Lion Up-To-Date Program but with in a few hours there was already some problems after those who tried to claim their free update ran in to a brick wall. Apple was fast to respond to this situation and said they would said replacement redemption codes out with in the next 3 days.
Today we are hearing that the replacement codes are for OS X Mountain Lion Server are being sent out instead of OS X Mountain Lion.
OS X Mountain Lion