Table '<0s>' is marked for deletion and was not added to the diagram.

A table that has been removed from the database diagram will be deleted from the database diagram when the changes are saved. The table will not, however, be deleted from the database.

For more information, see Remove a Table from a Database Diagram.

-or-

The table has been deleted from the database by another user and cannot be added to your database diagram.

For more information, see Delete a Table from a Database Diagram and the Database.