QueryVMField.VAPPNAME causes VCloudException

I am trying to use the QueryService's method QueryVmReferences(QueryParams) and I am getting an exception with a message 'Bad request: Unknown property name vappName.'

Here is the chunk of code that is causing the error:

            QueryService qs = VCloudClient.GetQueryService();

            QueryParams<QueryVMField> query = new QueryParams<QueryVMField>();

            query.Fields.Add(QueryVMField.VAPPNAME);

            query.Filter = new Filter(new Expression(QueryVMField.VAPPNAME, vAppRefs[0].name, ExpressionType.EQUALS));

            List<ReferenceType> vMRefs = qs.QueryVmReferences(query).GetReferences();

Am I doing something wrong? Any help would be greatly appreciated! Thanks.

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