This message means that the geometric tolerance references an invalid DRF. This problem can be due to a change to the model that caused datum features that the DRF references to become invalid.
If the referenced DRF is invalid, the best method for repairing a geometric tolerance is to repair the invalid DRF that it references. A DRF is often invalid because it references an invalid feature (the feature is missing surface references). Invalid DRF's and geometric tolerances in the model can usually be repaired by repairing the invalid features in the model. The best method for repairing a model with invalid objects is to repair invalid objects in the following order: