先把这个<%=SearchResultGrid.ClientID %>用引号引起来,然后你的后台代码GetPlanInDetailByPlanPageno应该在public void ProcessRequest(HttpContext context)方法中被调用,如:
public void ProcessRequest(HttpContext context){
context.Response.Write(GetPlanInDetailByPlanPageno(context.Request["planPageno"]));
context.Response.End();
}
用get试一试