Sys.WebForms.PageRequestManagerParserErrorException: The message received from the server could not be parsed

I fixed this issue. As I’m using UpdatePanel, I added below code in the Page_Load event of the page and it worked for me:

protected void Page_Load(object sender, EventArgs e) {
  ScriptManager scriptManager = ScriptManager.GetCurrent(this.Page);
  scriptManager.RegisterPostBackControl(this.btnExcelExport);
  //Further code goes here....
}