Surface Pro 2 can't boot to USB key
I have a WinPE 4 UEFI usb key that I created when we received the first Dell Windows 8 tablets, which works fine for those. The tablet will boot into our K2000 just fine. However, we just got a Surface Pro 2 which will not boot using the usb key. It recognizes it and attempts to load the boot files, but then I get the blue screen that says the signature of ahcix64.sys is not verified. I can't figure out why both tablets don't give me the error if there really is a problem with my bootable KBE.
Has anyone been able to boot a Surface Pro to their KBE? Was there any special steps that you needed to perform?