"file not found" when using Shell()

[secret_sauce]

Forgive if this is a total noob question.

All I want to do is launch an external app (a Perl script) using Shell(). But all I get is "Run-time error '53': File not found."

I even copied the example verbatim from the VB Help:

[VBA]Dim RetVal
RetVal = Shell("Macintosh HD:Applications:Calculator", vbNormalFocus)[/VBA]


Same error. This seems so elementary.