Hi,
the reported message is returned when you try to generate and run a project in which the Database node is missing. In fact if you perform the Find Model Problems task on the project you obtain the same error message.
To solve it you have to add a Database to the Domain Model, configure it and sync the Domain Model with the database (dbms).
For more details refer to the logic descripted here https://my.webratio.com/learn/learningobject/connecting-the-database-v-72.