I'm facing some troubles with my EF Model.

History: When my app was released in production a few years ago, my EF model was created via the Model First (edmx) technique. I works well on my production server with my SQL SERVER db.

Now I'm doing some improvements on my app, and I decided to leave the Model First technique to go on the Code first technique. It's working great on my localhost, but when I release my new app version on my production server and when my app tries to use the model I got this message:
CREATE DATABASE permission denied in database 'master'.

But I don't get it... My database still exists on my production server (since several years). Why does EF would like to create something? What can be wrong?

Thanks in advance for your answers.

EDIT:

Summary:

• For the same database on the same server
• For the same connectionstring
• For the same EF version (6)
• App with Model First works without problem
• App with Code First throw exception CREATE DATABASE permission denied in database 'master'.

BUT the database already exists. Why this error? Why does the code first version tries to create a database?