fout in domeincheck script

Ik heb een script gevonden op het internet om domeinnamen te checken.
Nu zit er een fout in regel 74 en ik kan niet uitvidnen wat het is...
de fout:
Notice: Undefined variable: sOutput in C:\apache\Apache2\htdocs\test\index.php on line 74
Hieronder de code:

<?
function whoislookup($sDomain)
{
$aDom = explode(".", $sDomain);
if(substr($sDomain, 0, 4) == 'www.' && count($aDom) >= 3)
{
$sDomain = substr($sDomain,4);
}
$sExt = strtolower($aDom[count($aDom) - 1]);
$aNic = array('ar','im','as','am','au','bt','bg','cl','cc','cg','bi','rw','zr','cr','cz','dk','ec','fo','gl','fr','de','ir', 'it','jo','my','mx','ni','nl','nu','pk','pl','ru','sg','sk','es','tw','th','to','tm','uk','ua','co','ch','li');
$aUS = array('com','net','org','info','biz');
$aRipe = array('il','gr','gg','je');
$aAPNic = array();
$aAUNic = array();
$aJPNic = array('jp');
if($sExt != "")
{
$iErrorLevel = 0;
if(in_array($sExt, $aNic))
{
$sServer = "whois.nic." . $sExt;
}
elseif(in_array($sExt, $aUS))
{
$sServer = "whois.networksolutions.com";
}
elseif(in_array($sExt, $aRipe))
{
$sServer = "whois.ripe.net";
}
elseif(in_array($sExt, $aAPNic))
{
$sServer = "whois.apnic.net";
}
elseif(in_array($sExt, $aAUNic))
{
$sServer = "whois.ausregistry.net.au";
}
elseif(in_array($sExt, $aJPNic))
{
$sServer = "whois.nic.ad.jp";
$sDomain = $sDomain . "/e";
}
elseif($sExt == "se")
{
$sServer = "whois.nic-se.se";
}
elseif($sExt == "lu")
{
$sServer = "whois.restena.lu";
}
else
{
$iErrorLevel = 2;
}
}
else
{
$iErrorLevel = 1;
}

if (!empty($sDomain) && $iErrorLevel == 0)
{
$fp = fsockopen("$sServer", 43, &$errno, &$errstr, 30);
if(!$fp)
{
$output = "$errstr ($errno)<br>\n";
}
else
{
fputs($fp,"$sDomain\n");
while(!feof($fp))
{
$sOutput = $sOutput . ereg_replace("\t", "&nbsp;", fgets($fp,128)) . "<BR>\n";
}
fclose($fp);
}
}
elseif($iErrorLevel == 2)
{
$sOutput = "Error $sExt for domain $sDomain is not a recognised extension<br>\n";
}
return $sOutput;
}
?>
<?
if(!isset($_POST['whois'])){
echo "
<form name=\"whois\" method=\"post\" action=\"".$_SERVER['PHP_SELF']."\">
<table width=\"500\" border=\"0\">
<tr>
<td width=\"111\">Domeinnaam:</td>
<td width=\"379\"><input name=\"domain\" type=\"text\" id=\"domain\" size=\"50\"></td>
</tr>
<tr>
<td>&nbsp;</td>
<td><input name=\"whois\" type=\"submit\" id=\"whois\" value=\"Whois\"></td>
</tr>
</table>
</form>
";
}else{
$domain = $_POST['domain'];
echo whoislookup($domain);
}
?>