Editing saved segmentations

When opening a saved segmentation scene and trying to edit it with the segment editor, the error message: “AttributeError: ‘NoneType’ object has no attribute 'GetNumberOfValues” appears.
Has anyone else experienced this error and knows how to deal with it?

Thanks!

Could you post the complete application log here?

What Slicer version did you use to create the scene and what Slicer version do open it with now?