Why did you start another thread asking the *SAME THING*???
In any case, *CLEARLY* you should be doing this in ASP.NET code and *NOT* using JavaScirpt. Period.
And there is NO REASON to use a <div> and then hide the <asp:TextBox> by hiding the <div>.
Instead, when you determine that you want to hide the form field yet still get its value when the <form> is posted, just use
<asp:HiddenField id="somename" runat="server" value="somevalue" />
<asp:TextBox id="somename" runat="server" value="somevalue" />
(And, by the way, you didn't even have the syntax for the textbox correct!! You set its value by assigning to a value=
attribute! Not as you were doing it.