can't step into A* Path Planning 's subvi

hi 

i am studying A* example for NIARC 2014

in the  "find path with a star.vi" ,why i coun't step into subvis like "get cell in path" or "a*".

and what i am trying to do is.

insert couple middle points. then show and compare the origianl path with the paths via through middle points in same interface.

thanks for help