Interoperability problem between a Java WebService and a C# Client

So I have made a WebService in JAVA.
This return an objet that containt two fields.
A BigDecimal and a String.
This object containts Assessors.

When I call a method from my webservice that return my object, I have interoperability problem.
In my C# Client, I can retrieve the String value, but cannot retrieve the BigDecimal value from my object. I have in the BigDecimal entry the null value.
I have the problem with the 2.0 Framework, but not with the 1.1 Framework, I can retrieve without problem my BigDecimal value. 

So I think, the problem come from the 2.0 framework because the generated classes containt Decimal<nullable> for 2.0 and Decimal for 1.1 Framework for my BigDecimal field.
How I can resolve this problem? 

I use Apache Tomcat 5.5 with Axis 1.2.1
It is possible to force the mapping in Visual Studio 2005 for the generated classes? Or the parametrize the WebService? 

Laurent