Does anyone know what the output of a Shell Command is?

Private Sub Command2_Click()
Dim fullstring As String
Dim iShell As String
fullstring = "Z:\NCOPY.EXE"
iShell = Shell(fullstring, vbMaximizedFocus)
MsgBox iShell, vbCritical
End Sub

The output of the MsgBox is -1720537 . Does this tell me anything? Can I use that for anything? What is it? If you have any info, or you have no clue, let me know. Thanks in advance!!

~Brian