I bought an MT-24EX for use on my 7D. When attached, only "TTL" and "M" show as modes on the flash. Also, in the menu on the 7D I can't access the External Flash settings. The camera says none is attached or is not compatible. Why would this happen?
This happens when the flash is not properly seated in the hotshoe. If it happens again, carefully check how the flash is sitting in the hotshoe.
I am glad you got it working but it may have just been a coincidence. The camera should automatically switch from wirless master to external flash when it senses a flash in the hotshoe.