Using JavaScript to Change Server-Side TextBox

[ftbadolato]

I have the following TextBox on my .aspx page.

<asp:TextBox ID="hdnresultbox" Style="z-index: 101; left: 520px; position: absolute;
top: 632px" runat="server" Width="1px" Height="1px" ReadOnly="false">no</asp:TextBox>

The JavaScript from viewing the source is as follows. There is some JS above what you see here, but it is working fine. I also have a try...catch around all of this. The error that occurs is [object Error] and it occurs on the lines below when I attempt to set the value of the text box. The text box is on the page, but I am thinking it may have something to do with the runat="server" in the code above. I need that though b/c I check the field in my code-behind file as well. I need help on updating the value of this field via JavaScript.

if(result == true){
document.getElementById('aspnetForm._ctl0_ContentPlaceHolder1_hdnresultbox').value='yes';
}else{
document.getElementById('aspnetForm._ctl0_ContentPlaceHolder1_hdnresultbox').value='no';
}

return result;