Hi gang, I'm having a bit of difficulty... for the life of me I can't get the AF assist on my 430EX II to fire when mounted to my 40D. I've made sure the custom functions on both the body and lens are set properly, but it still doesn't fire. If I stick the 430EX II on my Rebel G film camera, AF assist fires just fine.

Any insight? If its relevant, I recently bought this 40D in mint condition at a local camera shop as an upgrade to my T1i.

Thanks!