New Post: Formula issue after worksheet copy

I am facing the problem with the following

            var workbook = new XLWorkbook();
            var worksheet = workbook.Worksheets.Add("Sample Sheet");
            worksheet.Cell("A1").Value = "Hello World!";
            workbook.SaveAs(@"C:\");

it throws the exception at saveas, no matter what address i have been given there, please help it is just the start?

Delay in reply is great loss at my project end, please reply my both the posts?