Using Nonrowset-Based Messages in Service Operations Exposed as WSDL
If a nonrowset-based message is used in a service operation which will be exposed as a WSDL to third parties, the schema cannot be empty. The schema has to have at least the header elements, as shown in the following example:
<?xml version="1.0"?>
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"/>