relationships semantic model error

Hi
I'm trying to figure out why my model isn't giving me the information I need.
I have several tables for students, registered students and graduates.
I put the relations between students and graduation at (1-*) and between students, student-enrolled (1-*).
All three tables contain a single table called Number, which is the key and makes the connection.
When I try to display a the number that is in the graduation table and the name of the program, for example, Which student is enrolled, I get an error "Unable to complete relationships between fields." I don't know if I misdefined the relationships or well. However, when I put the cardinalities (several to many) between students, students-enrolled, it shows serious duplicates.
With you an idea of the problem please