Cifs cannot resolve SID

hi , (unresolved SIDs)

we have vnx5200 , the problem started two weeks ago we cant resolve the sid to names from the cifs server.

we made sure that all the potrs are open between the vnx to DOMAIN Controllers (both the DC's and the vnx reside in the same network subnet)

We also made sure that those SID's represent an existing user in Active Directory.

Thanks!