It's odd that you can make it work fine by selecting one column, but not two.
The "you have made changes to code that is not marked as editable" message is telling you that you are trying to make changes to an area of your page which has not been marked as editable in your template.
Have you tried opening your template and making a larger region editable? If it comes to it, you could make the whole content area editable while you apply your repeat regions, and return the template to how it was once you've done that.
