System.InvalidCastException: 'Unable to cast object of type 'ClassName' to type InterfaceName'.'

I am working on a C# application. I have a ClassLibrary type project which has an interface and some classes which implement this interface. Code is:

public interface IUserInterface
{
    String GetName();
    int Function(int a, int b);
}

public class UserClass : IUserInterface
{
    public String GetName() { return "Add"; }
    public int Function(int a, int b) { return a + b; }
}

public class UserClass1 : IUserInterface
{
    public String GetName() { return "Add"; }
    public int Function(int a, int b) { return a + b; }
}

public class UserClass2 : IUserInterface
{
    public String GetName() { return "Add"; }
    public int Function(int a, int b) { return a + b; }
}

My requirement is that i have to find all the implementations of IUserInterface, create the instances of those implementations using reflection and store all these instances in a List. My code for this is:

class Program
{
    private static List<Type> nameTypeDict = new List<Type>();
    private static List<IUserInterface> instances = new List<IUserInterface>();
    static void Main(string[] args)
    {
        Program obj = new Program();

        Assembly ass = Assembly.LoadFrom("ClassLibrary.dll");
        foreach (Type t in ass.GetExportedTypes())
        {
            if (t.GetInterface("IUserInterface", true) != null)
            {
                Console.WriteLine("Found Type: {0}", t.Name);
                nameTypeDict.Add(t);//Add to Dictonary
            }
        }

        foreach (var type in nameTypeDict)
        {
            var typeObject = Activator.CreateInstance(type);

            IUserInterface typeObj = (IUserInterface)typeObject;

            instances.Add(typeObject);
        }
        Console.ReadKey();
    }
}

I did manage to create the instance, but gets exception at

IUserInterface typeObj = (IUserInterface)typeObject;

The exception is:

System.InvalidCastException: 'Unable to cast object of type 'ClassLibrary.UserClass' to type 'ClassLibrary.IUserInterface'.'

How can this be resolved ? I know i am making some silly mistake but, i am unable to figure it out. The reason why i am casting it is because i have to save the instance in the IUserInterface type list.