Complex types from Java Axis Web Service not working in .Net

[dynoweb]

We have a return object that has a super class called
SoapReturnResponse. There are several implementing classes like User,
Card, DataTable (not the .net one). When we add the reference in VS
2003 and VS 2005 B2, VS is not able to type cast the more general type
SoapReturnResponse into it's actual type of User, Card etc..

For example:

SoapReturn soapReturn = billing.getUser(email);
if (soapReturn.returnStatus == 2) // expected response
{
SoapReturnResponse response = soapReturn.response;
User user = (User) response;
}

We get the error:
Cannot convert type
'WindowsApplication1.WebReference.SoapReturnRespon se' to
'WindowsApplication1.WebReference.User'

This works with PHP and Java Clients, can I get this to work in .Net or
do I have to do this differently?
The SoapReturnResponse contains an SoapReturnError object that has
several attributes and that seems to work just fine since it's a single
Object type.

The server is Tomcat v5 with Axis v1.3. We have customers that want a
..Net, PHP and Java web service client applications.

Any help with this would be greatly appreciated.

Included from the WSDL file if needed

<complexType abstract="true" name="SoapReturnResponse">
<sequence/>
</complexType>