primary trust relationship

I HAD 2 SERVERS IN MY LAB ON DIFFERENT DOMAINS ONE IS CAS ANOTHER ONE IS EUROPA
I AM ABLE TO ACCESS EUROPA SHARES FROM CAS.
BUT WHENEVER I TRY TO ACCESS CAS SHARE FROM
EUROPA SERVER I GIVES ERROR PRIMARY TRUST
RELATIONSHIP FAILS. WHATE CAN BETHE REASON.
AND IS THE SOLUTION SO THAT I CAN ACCESS.
EARLIER IN THE BEGINNING WHEN I INSTALLED CAS I WAS ABLE TO ACCESS IT FROM EUROPA. I HAD CHECKED ALL THE SHARES PERMISSIONS ALSO
AND SET FULL PERMISSIONS TO EVERYONE.