Why can't I reference System.ComponentModel.DataAnnotations?

Question

I\'m trying to use DataAnnotations in my WPF project to specify a maximum length of strings, with the following:

using System.ComponentModel.DataAnnotations;         


        

Answer 1

If you tried to update visual studio from vs2008 to vs2010. And your app uses framework 3.5 (and you don't want to upgrade it), and also used WCF RIA Services BETA... I have bad news... you MUST upgrade to WCF RIA Services v1 (BETA does not work on vs2010)... and due to this... you also have to install Silverlight 4 + upgrade to framework 4.0

See this: http://blog.nappisite.com/2010/05/updating-visual-studio-2008net-35-ria.html