asp.net - C# Web Forms navigation through pages error -

hello have tried found on internet "cross page postback".i succesfully transfer webform2 previous page null can not receive data webform1. here added webform1.aspx:

           <div>            <asp:textbox runat="server" id="txttransferid" visible="false"></asp:textbox>             <asp:button id="btntransfer" runat="server" postbackurl="~/webform2.aspx"/>           </div> 

here added webform2.aspx:

         <%@ previouspagetype virtualpath="~/webform1.aspx" %> 

here added webform2.cs:

        protected void page_load(object sender, eventargs e)         {             if (previouspage != null)             {                var id= ((textbox)previouspage.findcontrol("txttransferid")).text;             }         } 

i tried server.transfer async pageload time.

code on webform1.cs

            protected void btntransfer_click(object sender, eventargs e)             {               server.transfer("~/webform2.aspx");             } 

with webform2.cs code:

          protected async void page_load(object sender, eventargs e)           {               if (!page.ispostback)               {                 if (previouspage != null)                 {                 var id=((textbox)previouspage.findcontrol("txttransferid")).text;                 }                 var response = await apigetorderdetails(convert.toint32(id),1);                 dataset ds = (dataset)jsonconvert.deserializeobject(response,                  (typeof(dataset)));                 orderdetailgrid.datasource = ds;                 orderdetailgrid.databind();               }            } 

with server.transfer succesfully transfer webform2 , previous page not null can receive data webform1 error "system.web.httpexception: 'error executing child request /webform1.aspx

innerexception "invalidoperationexception: httpserverutility.execute blocked while waiting asynchronous operation complete."

at end tried @ webform1 :

         protected async void btntransfer_click(object sender, eventargs e)          {             await task.run(() => server.transfer("~/webform2.aspx"));          } 

the error went away grid wanted load never loaded.

any ideas please?thanks!