The Invalid Entity is issued in the following situations:

You must add attributes to this entity. How?

Select the Identifier attribute and change its data type to Integer or Text.

Select the Identifier attribute and change it to be mandatory.

Check your entity and choose which attribute must be sequential. In the other attribute, you have to un-check the Auto Number property. How?

Edit this entity and specify the Table Name property. How?

Edit one of these entities and change the Table Name property. How?

See Also

Add an Entity | Entity Attributes | Error Messages