Thank you for reporting this bug.
To eliminate this error, please delete this line in Private Sub InitUI in the Main module in the demo program. cbxSuperposCurves.cmbBox.Items.Add("5, 9, 10, 11, 12")
The program has been updated in the first post of the xGraph thread.
I have not changed the version number, because the bug was in the demo program and not in the class / library.