Error when I create form in model driven app

My dears

 I follow the steps in creating model driven app steps from Microsoft learning and the below is the link of the page 

https://docs.microsoft.com/en-us/learn/modules/how-build-model-driven-app/05-create-model-driven-app

but when creating Form and Save it I get this error 

what does it mean , and what can I do ?