Magento Fault Code 1没有其他信息

I am trying to use the Magento API to UPDATE a product. I am getting error code #1 with the following message:<b>Fatal error</b>: Uncaught SoapFault exception: [1] Internal Error. Please see log for details.

Below is my PHP that calls the service and should update three attributes. The Magento api documentation leaves a lot to the imagination so I am stuck

$ItemNmbr = $itemData->Item->ItemNmbr;
$ItemDesc = $itemData->Item->ItemDesc; 
$UnitPrce = $itemData->Item->UnitPrce;

$client = new SoapClient('http://website.com/store/api/?wsdl');

$session = $client->login('apiname', 'apipassword');
$result = $client->call($session, 'catalog_product.update', array(168, array(
    'description' => $ItemDesc,
    'price' => $UnitPrce,
    'weight' => $Weight
)));

var_dump ($result);

I am statically setting the ProductID above for now. Any information that will help me understand what I am doing wrong would be much appreciated.