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;