The solution provided by CaptainRon does work, but it also opens the form when the left button is clicked. I also encountered the shortcut menu opening with grayed if I ran the right click event two times in succession. So you might consider using the following code which disables the Form's shortcut menu when the right mouse button is clicked and opens the form in Dialog mode, then uses the Detail's MouseMove event to turn the shortcut menu back on.
Private Sub Detail_MouseMove(Button As Integer, Shift As Integer, X As Single, Y As Single)
Me.ShortcutMenu = True
End Sub
Private Sub TextBoxName_MouseDown(Button As Integer, Shift As Integer, X As Single, Y As Single)
If Button = acRightButton Then
Me.ShortcutMenu = False
DoCmd.OpenForm "FormName", , , , , acDialog
End If
End Sub
PaulF