Disable enable button inside gridview

<script type="text/javascript" src="Script/jquery-1.5.1min.js"></script>

<script type="text/javascript" language="javascript">

function toggleSelectionGrid(source) 
{
   var isChecked = source.checked;
   $("#GirdViewTable input[id*='chkLeave']").each(function(index) {
   $(this).attr('checked', false);
});
  source.checked = isChecked;
}

</script>

//on clock of ItemTemplate checkbox call able jQuery method
< asp:CheckBox ID="chkLeave" runat="server" onclick="toggleSelectionGrid(this);" />

protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e)
{
    if (e.Row.RowType == DataControlRowType.DataRow)
    {
        //Find the TextBox control.
        CheckBox Chek = (e.Row.FindControl(Chk) as CheckBox);
		if(Chek.Checked)
		{
        //Find the DropDownList control.
        DropDownList ddlCountries = (e.Row.FindControl("ddlCountries") as DropDownList);
        ddlCountries.Enabled=True;
		}
    }
}