getNextHighestDepth() problem

i have two movies, each with a movieclip on the _root level and this line of actionscript on the main timeline:

trace (clipName.getNextHighestDepth());

the only problem is, in one movie the trace returns ‘0’ (as i expected), but in the other it returns ‘undefined’ - which is strange, because as far as i can tell, the movies are identical in all but the actual names of the clips (and the shapes they contain, but that shouldn’t make a difference).

i’ve uploaded the two movies in case anyone wants to take a look. i’m sure i’m overlooking something really simple but i can’t see why one getNextHighestDepth() returns ‘undefined’.

test1.fla
test2.fla

thanks in advance

||| O ^ | + O ¬