Description of problem:
When I configured my cups to authenticate with Active Directory login and password, after some time working with cups web interface, I receive a popup that requires me to insert login and password. When I put my login and password the popup appears again.
In the /var/log/cups/error_log file I receive the following error:

E [12/Jun/2012:07:05:14 -0300] cupsdAuthorize: pam_authenticate() returned 7 (Authentication failure)!

And in the /var/log/secure file I receive the following error:

Jun 12 07:45:43 ServerName cupsd: pam_unix(cups:auth): authentication failure; logname= uid=0 euid=0 tty= ruser= rhost=  user=username


Version-Release number of selected component (if applicable):
Red Hat Enterprise Linux Server release 5.7 (Tikanga)
Cups 1.3.7

How reproducible:
There's not a step-by-step to reproduce the error, it just stop to authenticate. If I use the root password it works fine.

  
Actual results:
Authentication failure

Expected results:
Authentication

Additional info:
If I restart the cups daemon (service cupsd restart), the authentication starts working again.