The WSDL file is generated by SUN's jwsdp-1.6 and contains this complex type returned by a WS-call:
<complexType name="ServiceResponse">
<sequence>
<element name="errorCode" nillable="true" type="int"/>
<element maxOccurs="unbounded" minOccurs="0" name="errorMessages" nillable="true" type="string"/>
<element name="numRowsError" nillable="true" type="int"/>
<element name="numRowsSuccess" nillable="true" type="int"/>
<element name="numRowsWarning" nillable="true" type="int"/>
<element maxOccurs="unbounded" minOccurs="0" name="successMessages" nillable="true" type="string"/>
<element maxOccurs="unbounded" minOccurs="0" name="warnMessages" nillable="true" type="string"/>
</sequence>
</complexType>

The WS-Response contains an additional element 'errorMessagesAsString:
<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="
http://www.w3.org/2001/XMLSchema-instance">
<soapenv:Body>
<ns1:determinationOfDeterministicRequirementsResponse xmlns:ns1="http://planning.ws.fn.mbisoftware.biz">
<result>
<errorCode>-1</errorCode>
<errorMessages>invoke of the implementing class not implemented yet.</errorMessages>
<numRowsError>1</numRowsError>
<numRowsSuccess xsi:nil="1"/>
<numRowsWarning xsi:nil="1"/>
<successMessages xsi:nil="1"/>
<warnMessages xsi:nil="1"/>
<errorMessagesAsString>[invoke of the implementing class not implemented yet.]</errorMessagesAsString>
</result>
</ns1:determinationOfDeterministicRequirementsResponse>
</soapenv:Body>
</soapenv:Envelope>

There is a method 'public String getErrorMessagesAsString()' in class ServiceResponse, but it does not return a class property directly. It returns the errorMessages string array as one string.
So I think jwsdp is correct that it should not be in the soap response.