not be less than zero.
Parameter name: length— at System.String.InternalSubStringWithChecks(Int32 startIndex, Int32 length, Boolean fAlwaysCopy)
at System.String.Substring(Int32 startIndex, Int32 length)
at Copier.Form1.pageContent(HtmlDocument docc) in F:WorkCopierCopierForm1.cs:line 396
at Copier.Form1.scanItemPage() in F:WorkCopierCopierForm1.cs:line 335—System.String InternalSubStringWithChecks(Int32, Int32, Boolean)