Yeah, I've had trouble getting this right myself. My understanding is that the ObjectName refers to the name of the form itself not the name of the control for which the form is the SourceObject (but I could be wrong).
If all else fails you might try putting the code inside the subform itself as a Public Sub:
Public Sub sGoToLast()
DoCmd.GoToRecord , , acLast
End Sub
Let me know if that works.
Bill Norton
Austin, TX