Silverlight unit testing failing with could not load system.xml or one of its dependencies

I am developing a silverlight 4 application so to start with I created a silverlight test project. I compiled and ran without any code change and it worked just fine. Now I added a test, which reads xaml data and spit out a result. So I added system.xml and system.xml.linq but when I ran the test with these references, i am getting an error 'could not load file or assemble system.xml or one of its dependencies. I compared the version and runtime of xml and xml.linq against my test project and the silverlight project both are pointing to corr开发者_如何学Goect version and correct file. What am I doing wrong?

Thanks,

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** Found the problem, when I ran the project using silverlight test I do no thave the problem, I was trying to test it with TestDriven.Net that was the one causing the problem. *