Hi there,
I had the same issue but managed to fix it registering my button to send full postback. The problem lies in the fact that asynchronous postbacks are sent which means that the page on the client does not expect to receive an Excel document. Here is what you have to do to register your buttons:
protected override void OnPreRender(EventArgs e)
{
ScriptManager scriptManager = ScriptManager.GetCurrent(this.Page);
//ButtonExcelExport is the button firing the Excel download
scriptManager.RegisterPostBackControl(this.ButtonExcelExport);
base.OnPreRender(e);
}
Here is an interesting acticle about the PageRequestManagerParserErrorException :
http://weblogs.asp.net/leftslipper/archive/2007/02/26/sys-webforms-pagerequestmanagerparsererrorexception-what-it-is-and-how-to-avoid-it.aspxI found the answer to my problem here:
http://forums.asp.net/p/1040926/1596279.aspx