Class library can't find MembershipUser

I've added a class library project to my application.

In one of my classes, I need to use the MembershipUser class, but the project can't find it. I've added references to System.Web, System.Web.Security, and System.Security.Principal.

I'm开发者_运维技巧 not sure what the problem is. Has anyone run into this?

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If you are using .NET 4.0 you need to reference the System.Web.ApplicationServices.dll assembly. As always the documentation of the MembershipUser contains all the necessary information:

Namespace:  System.Web.Security
Assembly:  System.Web.ApplicationServices (in System.Web.ApplicationServices.dll)

In previous versions of the framework the MembershipUser class was located in the System.Web.dll assembly.