Your diagram will be updated with the following changes to match the database before the following tables can be loaded. (Visual Database Tools)
A table you are trying to add to the diagram is related to a table already on the diagram, and that relationship somehow contradicts the contents of your diagram. This occurs because another user has added or modified the relationship since you began working on the diagram.
Remember, when you add a table to a diagram, the Database Designer automatically includes any relationships between the existing tables and the newly added table. In attempting to add such a relationship, the Database Designer has discovered that your in-memory copy of the database structure no longer matches the contents of the database. Before adding the table, the Database Designer will update your diagram accordingly.
For example, suppose your diagram is initially consistent with the database. The diagram includes two tables, Student and Course, and a one-to-one relationship between them, called TutoringAssignment. The relationship indicates that each student can tutor a course and each course can be tutored by a student. Initially, your diagram includes no other tables.
While you are working on the diagram, another user changes the database structure. That user deletes the TutoringAssignment relationship and adds another relationship of the same name between the tables Student and SectionOfCourse. (This change improves the database structure, because it more faithfully represents your organization's information needs. Students are assigned to tutor particular sections of courses, not courses in general.) The other user commits these changes to the database.
Now you add the SectionOfCourse table to your diagram. Because this table has a relationship to the Student table already present on your diagram, the Database Designer tries to include this relationship on the diagram. The conflict arises because the to-be-included relationship has the same name as a now obsolete relationship already present on your diagram.
Because of these conflicts, the Database Designer will update your in-memory copy of the database structure accordingly. That is, it will remove the TutoringAssignment relationship between the tables Student and Course. Only then will the Database Designer add to your diagram the SectionOfCourse table and the TutoringAssignment relationship between the Student and SectionOfCourse tables.
The Database Designer does not reconcile all differences between your diagram and the database. It reconciles only those differences that would otherwise prevent you from adding the table to the diagram.