Devi lanciare una funzioncina Javascript al click lato client, attaccandola preventivamente al RadioButton:
PAGINA.ASPX
codice:
<head>
<script type="text/javascript">
function disabilitaTB()
{
var ID_CLIENT_TB = '<%= FindControl("IDServer_TextBox").ClientID %>'
document.getElementById(ID_CLIENT_TB).disabled = true;
}
</script>
</head>
<form id="form1" runat="server">
<div>
<asp:RadioButton ID="RB" runat="server" />
<asp:TextBox ID="IDServer_TextBox" runat="server"></asp:TextBox>
</div>
</form>
PAGINA.ASPX.CS (codebehind - nel Page_Prerender)
codice:
protected void Page_PreRender(object sender, EventArgs e)
{
if (!Page.IsPostBack) RB.Attributes.Add("OnClick", "javascript:disabilitaTB;");
}