Response.End() throwing error

Here is the alternate solution,

System.Text.StringBuilder sb = new System.Text.StringBuilder();
sb.Append(GetExcelXml(dsInput, filename));
response.Clear();
System.Web.HttpContext.Current.Response.AddHeader("Content-Disposition", "attachment;filename=" + fileName);
response.Write(sb.ToString());
Response.End();

Hope this may help you...

http://forums.asp.net/t/984756.aspx/1[^]

I know its very old question but may be helpful for others...

The Response.End method ends the page execution and shifts the execution to the Application_EndRequest event in the application's event pipeline. The line of code that follows Response.End is not executed.

Instead of Response.End(), use HttpContext.Current.ApplicationInstance.CompleteRequest()

string excelXml = GetExcelXml(dsInput, filename);
     response.Clear();
     response.AppendHeader("Content-Type", "application/vnd.ms-excel");
     response.AppendHeader("Content-disposition", "attachment;
     filename=" + filename);
     response.Write(excelXml);
     response.Flush();
     //response.End();
     HttpContext.Current.ApplicationInstance.CompleteRequest();

Source: Microsoft official website[^]

Replace response.End(); with HttpContext.Current.ApplicationInstance.CompleteRequest();