Getting the the error message : The requested method POST is not allowed for the URL /default.htm
<form onsubmit="return signup();" method="post" name="subform"  id="subform" action="">
  <table width="100%" border="0" >
  <tr>
    <td align="right" width="50%"> <div class="loginboxdiv" align="center">
   <input class="loginbox" name="email" type="text" />
   </div></td>
    <td align="left"  width="50%"><input type="image" value="submit" src="submitbutton.gif" width="128" height="24" /></td>
  </tr>
</table>
</form>

<script type="text/javascript" language="javascript">
function trim(str){str = str.replace(/^s*$/, '');return str;}
function signup() {
    var email   = trim($F("email"));
        //EMAIL VALIDATION
    var goodEmail = email.match(/b(^(S+@).+((.com)|(.net)|(.edu)|(.mil)|(.gov)|(.org)|(.info)|(.sex)|(.biz)|(.aero)|(.coop)|(.museum)|(.name)|(.pro)|(.arpa)|(.asia)|(.cat)|(.int)|(.jobs)|(.tel)|(.travel)|(.xxx)|(..{2,2}))$)b/gi);
    apos=email.indexOf("@");dotpos = email.lastIndexOf(".");lastpos=email.length-1;
    var badEmail    = (apos<1 || dotpos-apos<2 || lastpos-dotpos<2);
     if (email=="" || !goodEmail || badEmail) {
        $('.success').fadeIn(200).hide();
        $('.error').fadeOut(200).show();
        $("email").focus();
        return false;
    }
    else {

        var url = "optIn.php";
        var params =  $("subform").serialize();
        new Ajax.Request(url, {onException:showException, onFailure:showException, asynchronous:true, method:'post', evalScripts:false, postBody:params});
        $('.success').fadeIn(200).show();
        $('.error').fadeOut(200).hide();
        return false;
    }
}
function showException(req) {
    $("myResponse").innerHTML=req.responseText;
    alert("An error occured while talking to the server. Please try again.");
    $("loading", "myResponse").invoke('hide');
    $("submit").show();
    $("name", "email").invoke('clear');
}
</script>

<?php



$email  = trim($_REQUEST["email"]);



$pdbHost = "localhost";
$pdbUserName = "-------";
$pdbPassword = "------";
$pdbName     = "-----------";


//  Connect to mySQL
$conlink = mysql_connect($pdbHost, $pdbUserName, $pdbPassword);
if(!$conlink) {die('Unable to connect to '.$pdbHost);}
if (!mysql_select_db($pdbName, $conlink)){die('Cannot find database '.$pdbName);}

//SQL query
    $SQL2= "INSERT INTO lighthou_EmailAddresses.SubscriberEmails ( 'Email_Address`) VALUES ('".$Email."')";

    mysql_query($SQL2);

mysql_close($conlink);
?>