AD domain/forest function level support

The CIFS servers on the VNX behave as traditional Windows member servers in AD and can join AD 2003, 2008 and 2008 R2.  Going to 2008 R2 might infer changes in authentication for users - do you currently have any users (typically XP) authenticating with NTLM, not NTLM v2 or Kerberos?  That's worth a quick check.

Are you applying any GPOs in your domain to the CIFS servers?  You might want to do a little research and see if any GPOs are being applied.  You can start with server_security server_2 -info -policy gpo to show any GPO active against the CIFS servers.  Any field that says "Not defined" shows that there is no GPO being enforced:

[nasadmin@tstvnx~]$ server_security server_2 -info -policy gpo

server_2 :

Server compname: test_cifs_server

Server NetBIOS: TEST_CIFS_SERVER

Domain: apartment.net

Kerberos Max Clock Skew (minutes): 5

LAN Manager Auth Level: Not defined

Digitally sign client communications (always): Not defined

Digitally sign client communications (if server agrees): Not defined

Digitally sign server communications (always): Not defined

Digitally sign server communications (if client agrees): Not defined

NTLM SSP Minimum Client Security: Not defined

NTLM SSP Minimum Server Security: Not defined

Send unencrypted password to connect to third-party SMB servers: Not defined

Disable machine account password changes: Not defined

Maximum machine account password age: Not defined

... (more lines omitted)

Disable background refresh of Group Policy: Not defined

Restricted Groups: Not Defined

Group Policy Refresh interval (minutes): 90

Refresh interval offset (minutes): Not defined

GPO Last Update time (local): Wed Jan  9 17:24:15 EST 2013

GPO Next Update time (local): Wed Jan  9 18:54:15 EST 2013

Note that every 90 minutes, my server is checking for a new GPO, to see if one is out in AD waiting to be applied to it.

Let us know if that helps!