I suppose you are using
UpdatePanel
in your code. I have faced this issue, below code worked for me. See if it helps you. Add following code in the
Page_Load
event of your page:
protected void Page_Load(object sender, EventArgs e)
{
ScriptManager scriptManager = ScriptManager.GetCurrent(this.Page);
scriptManager.RegisterPostBackControl(this.btnExcelExport);
......
}