[CentOS] Samba3x daily logged errors with Win7 clients

In the course of upgrading from CentOS 5.4 to CentOS 5.5 I changed from 
using the samba (v3.0.x) packages to the samba3x (v3.3.8) packages, 
mostly because the newer version was said to better support Win7.  The 
Samba server services Linux, WinXP, and Win7 clients.

Now I get many, many errors logged to the Samba logs shortly after 3:00 
AM, but only from the Win7 clients.  I get roughly 430 sets of these 
messages in a twenty-second (!) period:

[2010/05/25 03:17:36,  1] smbd/service.c:make_connection_snum(748)
   create_connection_server_info failed: NT_STATUS_ACCESS_DENIED

These errors are never seen in the Samba logs that track the Linux and 
WinXP clients, only the Win7 clients.  I don't run virus scans or 
anything else (that I know of) on the Win7 machines in the middle of the 
night, but I do have the usual cron jobs running on the CentOS server 
around that time.  Could be related to log rotation or something like that?

I haven't seen a loss of connectivity, but then I don't use the client 
machines at 3:15AM.  If there is a brief connection failure I wouldn't 
know it.

I used my old (Samba 3.0.x) config file, user definitions and password 
database when I made the switch to the new (Samba 3.3.8) server and the 
newer code didn't seem to have any complaints with them.  The client 
shares seem to work without any problems.

Any thoughts on what could be generating all these errors?

Thanks.