Adding Reference Problem in Visual Studio 2010

I created my custom DLL "MongoDbExtensions". Now in a new project I add a reference to the "MongoDbExtensions" and then try to invoke a method inside the MongoDbExtensions called ToDocument. I use resharper to add the namespace at the top of the file but when I compile I still get the following error:

Error 1 The type or namespace name 'MongoDbExtensions' could not be found (are you missing a using directive or an assembly reference?) C:\Projects\HelpForum\DemoConsole\Program.cs 6 7 DemoConsole

What is going wrong? My DLL can be downloaded from here:

http://github.com/azamsharp/开发者_开发百科MongoDbExtensions/downloads

UPDATE 1:

Here is the MongoExtensions class:

namespace MongoDbExtensions
{

    public static class MongoExtensions
    {
        public static List<T> ToList<T>(this IEnumerable<Document> documents)
        {
            var list = new List<T>();

            var enumerator = documents.GetEnumerator();

            while (enumerator.MoveNext())
            {
                list.Add(enumerator.Current.ToClass<T>());
            }

            return list;
        }

}
}

ToDocument is an extension method that works on Object.

I repro. This DLL was built targeting .NET 4.0. You cannot use it in a project that targets anything else but the full 4.0 .NET framework. Either targeting a lower version or the client profile will produce this error.

Since your class is called MongoExtensions, you need to change MongoDbExtensions in your test project source code to MongoExtensions.