Autohotkey is unpredictable now (it used to work fine with wow all of the time) so I really wouldn't suggest using it. If you must, try one of the other free clients, or better yet just shell out the $3 a month for isboxer, it is definitely worth it.

I used ahk the first two times I attempted multiboxing (I did 4x druids to 60 in BC, and then a resto druid with a prot paladin during wrath). In cata I switched to isboxer and have never looked back. AHK is a great program for many things, but multiboxing just isn't its thing.