Help with Authorize(Roles=)] MVC 3 Windows Authentication

I am having problems with Authorize attribute in MVC 3 with Windows Authentication. When I decorate a controller with the [Authorize] attribute a specify a role, the Authorization always returns false when I know the user is 开发者_开发技巧a member of the role I specified. Am I missing something? Does anybody have some examples of how they used [Authorize] attribute in MVC 3 with Windows Authentication? Thanks for the help......

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[Authorize(Roles = "Admin")]

Should be enough