Unable to set the Orientation property of the PageSetup class

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C#

C#4.0

I have code for Generate Excel in c# it works fine in local but show error in server
and also work well for c# 2.0 in server

ExlApp.DisplayAlerts = false;
                WB = ExlApp.Workbooks.Open(EXLPath, MissVal, MissVal, MissVal, MissVal, MissVal, MissVal, MissVal, MissVal, MissVal, MissVal, MissVal, MissVal, MissVal, MissVal);
                WB.Activate();
                Microsoft.Office.Interop.Excel.Worksheet WS = (Microsoft.Office.Interop.Excel.Worksheet)WB.ActiveSheet;
                WS.PageSetup.Orientation = Microsoft.Office.Interop.Excel.XlPageOrientation.xlPortrait;
                WS.PageSetup.PaperSize = Microsoft.Office.Interop.Excel.XlPaperSize.xlPaperA4;
                WS.PageSetup.Zoom = false;
                WS.PageSetup.FitToPagesWide = 1;
                WS.PageSetup.FitToPagesTall = false;
                WS.PageSetup.RightMargin = ExlApp.InchesToPoints(0.2);
                WS.PageSetup.LeftMargin = ExlApp.InchesToPoints(0.2);
                WS.PageSetup.TopMargin = ExlApp.InchesToPoints(0);
                WS.PageSetup.BottomMargin = ExlApp.CentimetersToPoints(0.2);

Thanks