I am trying to copy data from DB-A to DB-B

I have created the table in DB-B; exactly that same as DB-A. It has a primary key on it. That key is EXACTLY the same on both.

When I insert into DB-B from DB-A it bombs out with a UNIQUE CONTRAINT error.

Q: How come the table in DB-A with the same exact primary key have data that does not meet the requirements of the primary key contraint ?