Explicitly defining ViewState of a server

Is it possible to explicitly define viewstate into a hidden field of an aspx page?

I tried this and got error

Exception Details: System.Web.HttpException: The state information is invalid for this page and might be corrupted.

<form name="Form1" method="post" action="" id="Form1" runat="server" >
<input type="hidden" name="__VIEWSTATE" id="__VIEWSTATE" value="/wEPD..............XCny" />
<input type="hidden" name="__EVENTVALIDATION" id="__EVENTVALIDATION" value="/wEdA..............ntw==" />

the error doesn't come when I postback to javascript alert function without runat="server" in form. But when I add runat="server" and call C# button_Click(object sender,EventArgs e) I get the invalid state error

thanks for any kind of help