David,
Offset 0 and size 1 is fine (these are normally used for paging through record sets, get 'size' records from offset 'offset').
You have made a small error that a few others have made - it's not obvious. When you create an AdminCountrySearch object from the classes generated from WSDL - you don't get the luxury of the default initialisation of certain fields (as you would if you instantiate the version of AdminCountrySearch in the konakartadmin.jar).
The result is that the Id field is set to 0. This means you're asking to search for country with id = 0.
You have to explicitly tell it not to use the Id field by setting it to -1 as follows:
AdminCountrySearch search = new AdminCountrySearch();
search.setTwoLetterCode("ES");
search.setId(-1); // KonakartAdminConstants.NOT_SET = -1
int offset = 0;
int size = 1;
AdminCountrySearchResult result = eng.getCountries(search, offset, size);
All the best,
Trevor