I can't figure this one out. I just have a standard checkout form that is hooked up to SagePay Server.
In the Store settings there is no mapping of billing firstname and surname but in the gateway class I can see the values being requested. When i submit the form, I get the message saying "3107 : The BillingSurname field is required."
If I amend the gateway class to hardcode values in the field it goes through fine. What makes it even stranger is that on a live site using the same codebase and database, it all goes through to SagePay without any errors at all.