Try this
<div id="divval" onclick="CheckStat();" >
<asp:TextBox ID="txtTest" runat="server" ></asp:TextBox>
</div>
<script type="text/javascript" language="javascript">
function CheckStat() {
var txtId = document.getElementById('<%=txtTest.ClientID%>');
alert(txtId.disabled);
if (txtId.disabled == true) {
txtId.disabled = false;
}
else {
txtId.disabled = true;
}
}
</script>
If you click outside, near textbox, it will work. You can adjust the UI