DateTimeOffsetAdapter interfering with WCF serialization of DateTimeOffset objects

Question

I have a WCF service reference (= client proxy) generated by Visual Studio 2008 (.net 3.5 sp1). The generated code contains a data contract with DateTimeOffset properties so naturally VS decorated it with KnowTypeAttribute(System.DateTimeOffset).

Whenever I invoke a WCF operation that returns the above mentioned data contract, I get the following exception:

Type 'System.DateTimeOffset' cannot be added to list of known types since another type 'System.Runtime.Serialization.DateTimeOffsetAdapter' with the same data contract name 'http://schemas.datacontract.org/2004/07/System:DateTimeOffset' is already present

I understand that DateTimeOffsetAdapter is a struct in System.Runtime.Serialization that is used when serializing DateTimeOffset objects. So why does it cause this exception and how can this be fixed or avoided?

Answer 1

In my case the issue seemed to stem from having .Net 4 installed prior to adding IIS as a feature to Windows 7.

A colleague and I fixed the issue by opening an elevated (Run As Administrator) command prompt. Then ran the following:

cd C:\Windows\Microsoft.NET\Framework64\v4.0.30319
aspnet_regiis.exe -i

Hope this helps someone!

Answer 2

I don't know why. But to solve the problem try to migrate your project to .NET Framework version 4