org.owasp.webscarab.plugin.webservice.Schema.java does not appear to support constructs like this:
<element name="ResultaatCode" type="xsd:int"/>
<element name="ResultaatBericht" type="xsd:string"/>
<element name="Matchnummer" type="xsd:long"/>
because line 107 assumes an element to have a 'type' attribute and line 85 assumes a complexType to have a 'name' attribute.
I haven't checked the XML Schema docs to see if these assumptions are valid (actually I suspect they are not), but even if they are it would be nice if a specific error message could be generated. Currently a NPE is written to the console.