If you're on iTunes 12.1 or 12.1.1 you'll have to downgrade to 12.0.1. This guy has a great step by step of how to totally wipe itunes and then jailbreak.
I had the same problem until I followed his instructions. Now my iPad mini is jailbroken.
Next is my 6 plus.
Good luck
Downgrading isn't 100% required. Worked fine for me on Windows 8.1 Professional x64 and iTunes 12.1.0.71 x64. Had to install the 3rd download from http://www.3kzhushou.com/edu/792.html that TaiG itself linked to.