authentificate user can admin printer not work

[Stéphane Purnelle]

Hi,

I have a little problem.
For the admin section of cups, I setting up cupsd.conf for verify user included in a group.

.....
<Location /admin>
  AuthType Basic
  AuthClass Group
  AuthGroupName Prtoper

  # Encryption Required
  Order Deny,Allow
  Deny From All
  Allow localhost
  Allow From x.x.x.x/xx.x.x.0
</Location>
.....

Prtoper is a group which is stored in a ldap server (openLDAP)
getent group prtoper work fine !

But when the user/password dialog box appear and I have typed user and password, the dialog box re-appear (same as password not correct).

In error_log, I can read :
cupsdAuthorize: pam_authenticate() returned 9 (Authentication service cannot retrieve authentication info.)!

anyone could help me ?

Version : cups 1.2.1.

Stéphane Purnelle