Just something I noticed; seems strange to me; might be nothing, but & on my keyboard (US) lives on the 7 key; so to get CTRL+ALT+& you would also have to hold down SHIFT as well as CTRL+ALT as you press the 7 key.

Perhaps try it on F6 without any modifiers and see if it works?

I don't have ISBoxer in front of me, but I think you need two keys, one to activate it and one to bind the macro to in WoW, these don't necessarily have to be the same.

Maybe that helps somewhat?