The 'parameter' element default value 'NULL' is not a ...

I am getting the following problem when trying to setup a WSDL for my project.

Error Loading WDSL
There was something wrong with the WDSL you are trying to import

Source: null
Error: The 'custref' element default value 'NULL' is not a valid value for 'VuCustRef@http://service.secure-foo-bar.com/soa/soap/'

Wed Feb 01 15:02:17 CET 2012:ERROR:org.apache.xmlbeans.XmlException: error: e-props-correct.2: The 'custref' element default value 'NULL' is not a valid value for 'VuCustRef@http://service.secure-foo-bar.com/soa/soap/'
org.apache.xmlbeans.XmlException: error: e-props-correct.2: The 'custref' element default value 'NULL' is not a valid value for 'VuCustRef@http://service.secure-foo-bar.com/soa/soap/'
at org.apache.xmlbeans.impl.schema.SchemaTypeSystemCompiler.compile(SchemaTypeSystemCompiler.java:225)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.apache.xmlbeans.XmlBeans.compileXmlBeans(XmlBeans.java:667)
at org.apache.xmlbeans.XmlBeans.compileXsd(XmlBeans.java:553)
at com.eviware.soapui.impl.wsdl.support.xsd.SchemaUtils.buildSchemaTypes(SchemaUtils.java:287)
at com.eviware.soapui.impl.wsdl.support.xsd.SchemaUtils.loadSchemaTypes(SchemaUtils.java:194)
at com.eviware.soapui.impl.support.definition.support.XmlSchemaBasedInterfaceDefinition.loadSchemaTypes(XmlSchemaBasedInterfaceDefinition.java:79)
at com.eviware.soapui.impl.wsdl.support.wsdl.WsdlInterfaceDefinition.load(WsdlInterfaceDefinition.java:61)
at com.eviware.soapui.impl.wsdl.support.wsdl.WsdlContext.loadDefinition(WsdlContext.java:66)
at com.eviware.soapui.impl.wsdl.support.wsdl.WsdlContext.loadDefinition(WsdlContext.java:30)
at com.eviware.soapui.impl.support.definition.support.AbstractDefinitionContext.cacheDefinition(AbstractDefinitionContext.java:268)
at com.eviware.soapui.impl.support.definition.support.AbstractDefinitionContext.access$400(AbstractDefinitionContext.java:44)
at com.eviware.soapui.impl.support.definition.support.AbstractDefinitionContext$Loader.construct(AbstractDefinitionContext.java:235)
at com.eviware.soapui.support.swing.SwingWorkerDelegator.construct(SwingWorkerDelegator.java:46)
at com.eviware.soapui.support.swing.SwingWorker$2.run(SwingWorker.java:149)
at java.lang.Thread.run(Thread.java:680)
Wed Feb 01 15:02:17 CET 2012:ERROR:com.eviware.soapui.impl.wsdl.support.xsd.SchemaException
com.eviware.soapui.impl.wsdl.support.xsd.SchemaException
at com.eviware.soapui.impl.wsdl.support.xsd.SchemaUtils.buildSchemaTypes(SchemaUtils.java:297)
at com.eviware.soapui.impl.wsdl.support.xsd.SchemaUtils.loadSchemaTypes(SchemaUtils.java:194)
at com.eviware.soapui.impl.support.definition.support.XmlSchemaBasedInterfaceDefinition.loadSchemaTypes(XmlSchemaBasedInterfaceDefinition.java:79)
at com.eviware.soapui.impl.wsdl.support.wsdl.WsdlInterfaceDefinition.load(WsdlInterfaceDefinition.java:61)
at com.eviware.soapui.impl.wsdl.support.wsdl.WsdlContext.loadDefinition(WsdlContext.java:66)

This PHP code can access the WDSL just fine:

$soapClient = new SoapClient( "https://service.foo-bar.com/soa/soap/?WSDL",
array( "exceptions" => true,
"cache_wsdl" => WSDL_CACHE_NONE,
"login" => $authUser,
"password" => $passphrase));