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
The Current Status Of The iOS 6.1 iPhone 5 Jailbreak
Apple are expected to release iOS 6.1 GM to developers today as the current beta 4 expires in only 2 days.
Ever since Apple have released iOS 6 jailbreaks have been working hard to find a useable exploit to use and it appears they have found one which is usable but they still are holding out until Apple release iOS 6.1. They are doing this to be absolutely certain that the method has not been patched in the update.
It now seems that the Jailbreak team have done their work and are waiting for Apple to step up to the game and release iOS 6.1.