Why is is that I get a return value when I look for a Window Name that is 2 characters long but when I go larger I get a return of 0?

Code:
Private Sub Command1_Click()
    'gets rid of any running instance of the program
    Dim CloseIt As Long
    CloseIt = FindWindow(vbNullString, "IA") ' This WORKS!
    'CloseIt = FindWindow(vbNullString, "METOO")' DOESN'T WORK! 
    PostMessage CloseIt, WM_CLOSE, 0&, 0&
End Sub