This means that the Checkbox set selector should be used to set the value(s) of a many to many association. In the association box, you have selected the same entity as the dataview. You should change either the dataview entity or the association in the checkbox.
As an example, lets say you wanted to select valid processing locations for an order. You would create a dataview for entity order and then in a checkbox set selector, you would point to the association between order and processinglocations entities.
Hope that helps,