visual studio 2010 - VS2010 target .net 2.0 and System.Runtime.Serialization -

Why can not I add a reference to the system? Runtime Serialization, while targeted 2.0?

In addition to this, if I change the 2005 project using the system. From time to time. Virtualization vs2010 conversion fails with a build error.

I am using the data contract class and the compiler says

the type or name space name 'datacontact' could not be found (whether you use the Director or Assembly Reference Do not miss?) C: \ Users \ My \ ClassLibrary1 \ Class1.cs 8 6 Class Library 1

< P> The reason for this is that you need to use .NET 3.5 to use DataContracts, those items that are present with .NET 3.5 So you must target that goal version.

Here is an MSDN that talks about one aspect of Data Contracts and .NET version.