This way
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title></title>
<script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/1/jquery.min.js"></script>
<script type="text/javascript">
function Toggle() {
$("#enable").live("click", function () {
$("#table tr:last input").removeAttr("disabled");
});
$("#disable").live("click", function () {
$("#table tr:last input").attr("disabled", "disabled");
});
}
</script>
</head>
<body onclick="Toggle(this, event)" style="height: 900px; width: 900px">
<form id="form1">
<input type = "button" id = "disable" value = "disable" />
<input type = "button" id = "enable" value = "enable" />
<table id = "table">
<tr><td></td></tr>
<tr style="background-color: #F7DFB5; color: #8C4510;">
<td >
</td>
<td >
<input type="text" size="20" maxlength="25" name="ctl00$contentPlaceHolder$Gr_Form$ctl22$No_F_En"
id="ctl00_contentPlaceHolder_Gr_Form_ctl22_No_F_En" />
</td>
<td >
<input type="text" size="20" maxlength="20" name="ctl00$contentPlaceHolder$Gr_Form$ctl22$txt_F_Na"
id="ctl00_contentPlaceHolder_Gr_Form_ctl22_txt_F_Na" />
</td>
<td >
<input type="text" size="20" maxlength="20" name="ctl00$contentPlaceHolder$Gr_Form$ctl22$txt_F_sur"
id="ctl00_contentPlaceHolder_Gr_Form_ctl22_txt_F_sur" />
</td>
<td >
<input type="text" size="12" maxlength="12" name="ctl00$contentPlaceHolder$Gr_Form$ctl22$No_F_Mob"
id="ctl00_contentPlaceHolder_Gr_Form_ctl22_No_F_Mob" />
</td>
<td >
<input type="text" size="40" maxlength="40" name="ctl00$contentPlaceHolder$Gr_Form$ctl22$txt_F_Email"
id="ctl00_contentPlaceHolder_Gr_Form_ctl22_txt_F_Email" />
</td>
<td >
<input type="submit" name="ctl00$contentPlaceHolder$Gr_Form$ctl22$Bu_Save" value=""
id="ctl00_contentPlaceHolder_Gr_Form_ctl22_Bu_Save" class="Save" />
<input type="submit" name="ctl00$contentPlaceHolder$Gr_Form$ctl22$Bu_SearStd" value=""
id="ctl00_contentPlaceHolder_Gr_Form_ctl22_Bu_SearStd" class="Find" />
</td>
</tr>
</table>
</form>
</body>
</html>
Demo
