Just discovered something. There are a few tables with DatabaseB that i can access from DatabaseA, but not all tables.
For example, there is TableA, TableB, TableC, and TableD in DatabaseB. Out of which TableB and TableD can be queried from DatabaseA using
USE DatabaseA
GO
SELECT * from DatabaseB.User.TableB
GO
SELECT * from DatabaseB.User.TableD
GO
which is sucessful. And
USE DatabaseA
GO
SELECT * from DatabaseB.User.TableA
GO
SELECT * from DatabaseB.User.TableC
GO
fails.