You have to use the other "Execute program" function, the one with an "evaluated" pathname, and pass either only the filename alone (= microM8, no pathname nor .app extension), or Apppath + "filename". I just tested with the filename alone and this worked fine: (well I used another application than yours but I guess your microM8 works)
PS: If you include the other app in your application, put it in the Resources folder.
* Collision between Active 2 and Active
Sound : Play sample a2beep
Special : Execute external program "microM8"""