How to use an IEnumerable<T> business object as RDLC datasource, the way it REALLY works?

Question

I have the hardest time creating an WebForms RDLC report with my business objects, in Visual Studio 2010. I am using the designer to build my report.

In the Report Data View of VS2010 I select New/Dataset... Strange enough, the Data Source Configuration Wizard immediately pops up, covering the Dataset Properties dialog.

When I cancel the Wizard, I am able to manipulate the Dataset Properties dialog somewhat, but none of my business objects does show up. Actually, nothing selectable shows up at all.

What do I need to have my business object selectable?

Note: Earlier in the project, this once worked. I must have changed something, but what?

I have read this question, but my Dataset is in the same project, on the ASPX-Page's code behind file. I have set it up like so:

    public IEnumerable<MyDto> Getxy() {
        return new List<MyDto>(); //TODO later use real data.
    }

I have also read this one but my object already matches what's suggested there. It is a really simple POCO DTO's with no constructor (which makes it automatically have a public parameterless constructor)