A System.InvalidOperationException exception may occur when you try to use a Visual Studio .NET 2003 client application against a SQL Server 2005 native Web service
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Source: Knowledge Base
Product: Microsoft SQL Server 2005 Standard Edition
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A System.InvalidOperationException exception may occur when you try to use a Visual Studio .NET 2003 client application against a SQL Server 2005 native Web service
http://support.microsoft.com/kb/907886/en-US