Castle Interceptor to Selectable interface

Question

public interface ISelectable
{
    bool Selected { get; set; }
}

public class Selectable : ISelectable
{
    #region ISelectable Members

    public virtual bool Selected { get; set; }

    #endregion
}

[Behavior(0, typeof(ISelectable))]
public class SelectableBehavior : IInterceptor
{
    #region IInterceptor Members

    public void Intercept(IInvocation invocation)
    {
        if (invocation.Method.DeclaringType.Equals(typeof(ISelectable)))
        {
            if (invocation.Method.Name.Equals("get_Selected"))
            {
                invocation.ReturnValue = (bool)invocation.Arguments[0];
            }

            invocation.Proceed();

            //if ("set_Selected".Equals(invocation.Method.Name))
            //{
            //    invocation.Method.Invoke(invocation.InvocationTarget, invocation.Arguments);
            //}
        }
        else
        {
            invocation.Proceed();
        }
    }

    #endregion

}

i have the above interface, class and Interceptor and the following class

public class Entity
{}

and i have register the Interceptor via Castle container

Entity e = ServiceLocator.Current.GetInstance<Entity>();

when trying to

((ISelectable) a).Selected = true;

I get the following error

System.NotImplementedException : This is a DynamicProxy2 error:
the interceptor attempted to 'Proceed' for method 'Void set_Selected(Boolean)'
which has no target. When calling method without target there is no implementation
to 'proceed' to and it is the responsibility of the interceptor to mimic the
implementation (set return value, out arguments etc)

Please help