The {0} {1}' contains a wrong number of DataCells per DataRow element. {2} DataCells per DataRow element are expected, because ...

The {0} ‘{1}' contains a wrong number of DataCells per DataRow element. {2} DataCells per DataRow element are expected, because there must be as many DataCell elements as there are leaf-node DataGroupings (i.e. DataGrouping without sub-groupings).