Hi,
What is happening is the following:
1. You did create some entities.
2. You published your module.
3. You changed the Id of one of the entities, that was autonumber to not be autonumber.
4. You try to publish, and it fails with that warning.
In OutSystems, you can't change, or replace, the Identifier, after you published the entity.
The easiest solution is to create a new entity with the changes to the attribute, and replace the old one by this.
But this does not work as smoothly if you have data in this entity (in any environment), and you want to keep the data. In this case you can't delete the old, and need to prepare some kind of data migration to be executed after publishing.
What's exact your needs relative to keep existing data?
Cheers