Searching by Customer Category

Is it possible to search via the Customer Category? I can do it in the web UI, but when I try it in the web service, I get "you need to provide a valid search operator".

Here's a code snippet of what I'm trying to do:

CustomerSearch custSearch=new CustomerSearch();
CustomerSearchBasic customerSearchBasic = new CustomerSearchBasic();
RecordRef rtl=new RecordRef();
rtl.setName("Retail Customer");
rtl.setInternalId("1");
rtl.setType(RecordType.customerCategory);
RecordRef[] cats={rtl};
customerSearchBasic.setCategory(cats);
custSearch.setBasic(customerSearchBasic);
SearchResult result=port.search(custSearch);

Thanks. I'm new to this web service