First of all, don't use the original "WoW Macro Action" as this will make it harder for you to manage, and understand the management of, the WoW macros in ISBoxer. It's still available for backwards compatibility and because some people are used to it, but anything new should probably use the new system instead (this will become more obvious with future ISBoxer updates...)

Instead use the WoW macro library, which is under Game Helpers, along with a Named World of Warcraft Macro Action. This will give you better control over who has what macros, and the interface should be easier to use/follow since it's not all crammed together like the WoW Macro Action. For a more specific example that directly relates to this thread, the Preview tab in the WoW macro library is easily understood and operated, whereas the "Final macro text" at the bottom of a WoW Macro Action confuses the shit out of people. (It's the same thing).

In other words, by using the WoW Macro Library you should have an easier time making sure the macro is available on a particular character, and that it has the right commands in it. See if switching helps.

(also, try another hotkey. combinations of F11 and F12 are used by some ISBoxer macros under Quick Setup 38, you can see them all there)