Probably because your toRango contains only one cell. You cannot set inside borders in the single cell.

>Hola
>
>I’m receiving the next error while trying to set the LineStyle property for an Excel range of cells:
>
>(Translated from Spanish: )
>
>OLE dispatch exception code o of ?:?
>
>
>
>My pieces of code is:
>
>WITH toRango.Borders(12) && Horizontal Interno
> .LineStyle = 1 && Error triggers here
> .Weight = 3
>ENDWITH
>
>The error does not happen when setting the LineStyle property of several other borders like:
>toRango.Borders(9), toRango.Borders(10), etc.
>
>I'll appreciate any hints.
>
>Thanks in advance and regards.
>
>Oscar Corte