Problem while creating CreditMemo

Hi,
   When we are trying to create a credit memo (Webservices 2.5 version) it is giving the error as
      Error Code:    INVALID_KEY_OR_REF
      Error Message : The Specified key is invalid.
  I have given the code below.
     this.login(true);
     CreditMemo cmo = new CreditMemo();
     cmo.altHandlingCost = 1000.00;
     cmo.altHandlingCostSpecified =true;
     cmo.altShippingCost = 1500.00;
     cmo.altShippingCostSpecified =true;
     cmo.balance = 3000.00;
     cmo.balanceSpecified =true;
     cmo.exchangeRate  = 10.0;
     cmo.exchangeRateSpecified =true;
     RecordRef r = new RecordRef();
     r.internalId ="-5";
     r.name="Wolfe Electronics";
     r.type = RecordType.customer;
    cmo.entity  = r ;
    cmo.externalId ="7HCRMEMO001";
    recordRef rloc = new RecordRef();
    rloc.internalId ="1";
    rloc.name ="Warehouse - East Coast";
    rloc.type = RecordType.location;