Error in Debtor_FindByName ??

Hi Experts,

When i am trying to create Debtor through Debtor_FindByName(arg),

 $debtor = $this->client->Debtor_FindByName(array(
          'name' => $data['firstname']
        ))->Debtor_FindByNameResult->DebtorHandle;

i am getting  NOTICE : undefine symbol DebtorHandle

StdClass::$DebtorHandle

What is wrong with the above code..

Can any one drive me ??

Thanks in advance .