[Samba] problem connecting to shares from Win7 clients - invalid NTLMSSP_MIC

[Sonic]

Domain users using Windows 7 systems lose the ability to connect to
Samba shares. Some users can connect one day but then lose the ability
the next.

When the problem starts to occur the log.smbd displays:
===============================================
  check_ntlm_password:  authentication for user [user1] -> [user1] ->
[MYDOMAIN\user1] succeeded
  ntlmssp_server_postauth: invalid NTLMSSP_MIC for user=[user1]
domain=[MYDOMAIN] workstation=[MACHINE]
===============================================

The file server in question is running Version 4.5.2-GIT-0d08df6
The PDC (a different server) is running Version 3.6.24-SerNet-Debian

Connecting using smbclient from two other Samba installations, one
running 3.6.22 and one running 3.6.19 work fine.
The log.smbd just displays the first line from the two above for
smbclient connections as well as the currently working users from
their Win7 boxes.
===============================================
  check_ntlm_password:  authentication for user [user1] -> [user1] ->
[MYDOMAIN\user1] succeeded
===============================================
There is no foillow-up postauth error in these cases.

Assistance is appreciated.

Thank you,

Chris