SQL Server Permission Denied Error When I'm DBOwner?
From what I see you created a server login with server roles (DBCreator and SecurityAdmin are server roles). But this doesn't mean it already has privileges on an existing database.

What you need to do is to create a user in that database and map it to the login:

use your_db
create user x for login y
exec sp_addrolemember 'db_owner', 'x'


This will assign your new user the database role db_owner to the database. Now you should be able to create tables with the login. You can try also other roles, if you don't need to be the db owner.