Custom group box not binding to bindingsource

I need to bind a GroupBox to a BindingSource, which in turn is bound to the following object:

public class CustomerType
{
    public int Id {get; set;}
    public string Name {get; set;}
    public MemberType MemberType {get; set;}
}

public enum MemberType {Adult, Child}

I followed this answer to create a custom GroupBox. I also set the data bindings as follows:

groupBoxMemberType.DataBindings.Add("Selected", this.bindingSource, "MemberType");

However, when loading an existing object, I get the following exception:

DataBinding cannot find a row in the list that is suitable for all bindings.

The exception occurs when setting the data source:

customerType = customerTypeRequest.Load(id);
bindingSource.DataSource = customerType;  //raises exception

What am I missing? Is there an alternative to get radio buttons to bind to a datasource, specifically a BindingSource?