XmlBeans - Web service - BindingException

Hi,
I am working with XmlBeans in Jbuilder and have created a project that contains a couple of EJBs that use XmlBeans to compile and manipulate a couple of XSD Schema files. The application works fine when deployed to Weblogic as an EJB, however when I configure the project as a Web Service and rebuild I get the following error:

[servicegen] weblogic.xml.schema.binding.BindingException: Invalid class received: interface com.bt.sas.SasSendDocument loaded from file:/D:/CLASSPATH/XmlBeanProject/xmlTypesSasSend.jar!/com/bt/sas/SasSendDocument.class. All classes that will be serialized or deserialized must be non-interface, non-abstract classes that provide a public default constructor

As I hinted above I am instantiating the interface "SasSendDocument.class" in my JBuilder project and can deploy and run the application but when I try and create a web service from the project it starts complaining about the fact that I am using an interface. XmlBeans "scomp" also generated a SasSendDocumentImpl.class that I have tried to use to overcome this problem (althoughin WLWorkshop I have always used the XmlBeanDocument object), but I then get the following error:

[servicegen] weblogic.xml.schema.binding.BindingException: No default constructor was found for class com.bt.sas.xml.impl.SasResultDocumentImpl loaded from file:/D:/Classpath/SasReturnSrc.jar!/com/bt/sas/xml/impl/SasResultDocumentImpl.class.All classes that will be serialized or deserialized must be non-interface, non-abstract classes that provide a public default constructor - with nested

Here it seems to be complaining that the class has no default constructor. However, these classes are auto-generated by XmlBeans for me and I don't believe I should have to tinker with the source and recompile. Anyway, even if I do change the class I cannot update the .xsb files which were produced by the XmlBeans compiler.

Any ideas greatfully received

Regards
Davy