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
Evasi0n 1.4 Will Allow You To Jailbreak iOS 6.1.2
Earlier today Apple released iOS 6.1.2 to the public and it appears they have still not patched the exploit used in the evasion jailbreak.
As you may have guess that means that Evasi0n 1.4 which is expected to be released in the next few hours will allow you to jailbreak your device running iOS 6.1.2
If you want to find out how to Jailbreak your iPhone, iPad or iPod touch we have got a full video tutorial here