Hello Umapathi,
I have created a sample HTML using JQuery to show you how it is done.
<html>
<head>
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js" type="text/Javascript"></script>
<script type="text/JavaScript">
function enableName(ctrl, txtId) {
if (ctrl.checked)
$('#' + txtId).removeAttr('disabled');
else
$('#' + txtId).attr('disabled', 'disabled');
}
</script>
</head>
<body>
<form action="demo_form.asp">
First name: <input type="text" name="fname"><br>
Last name: <input type="text" name="lname" id="lname" disabled><input type="checkbox" id="chkName" name="chkName" onclick="enableName(this, 'lname');"/><br>
<input type="submit" value="Submit">
</form>
</body>
</html>
</br></br>
Basically you will have to use javascript code similar to shown below to enable the textbox.
$('#' + txtId).removeAttr('disabled');
To again disble the textbox use javascript code similar to shown below.
$('#' + txtId).attr('disabled', 'disabled');
Also from your code I suggest that you use direct ID of the textbox rather than using closest & find. Remember ID's are unique in a page. i.e. No two controls should have same id.
Regards,