You are trying to use Windows Forms functionality in a ASP.NET Web Page. Line 140:
FileDialog fldlg = new OpenFileDialog();
Windows Forms is desktop technology. You can't mix that with a ASP.NET web app. You can use the FileUploadControl to enable file uploads in your web application:
http://msdn.microsoft.com/en-us/library/system.web.ui.webcontrols.fileupload.aspx