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
iOS 6.1 GM Expected To Be Released Tomorrow
Apple released the first developers beta of iOS 6.1 back in November and developers are now on beta 4 which was seeded back in December a point to remember about beta 4 is that it expires on Sunday evening.
Usually we would see Apple release the next beta or the GM to developers at least a few days before the current beta is set to expire but that does not seem to be the case with iOS 6.1
At this moment we are 99% certain we will see the iOS 6.1 Gold Master released to developers at some time tomorrow leading to a public release sometime next week.