I have a simple c# application

Excel.Application excelApp = new Excel.Application();
excelApp.Visible = true;
string workbookPath = "/book.xls";
excelApp.Application.Workbooks.Open(workbookPath,
Type.Missing, Type.Missing, Type.Missing, Type.Missing,
Type.Missing, Type.Missing, Type.Missing, Type.Missing,
Type.Missing, Type.Missing, Type.Missing, Type.Missing,
Type.Missing, Type.Missing);


excelApp.Cells[1, 1] = TextBox1.Text;

When I run it from VS development Server it open Excel file Ok, but when I
put it in virtual directory it runs excel.exe process and shows nothing, no
errors

what can it be?
thanks