Kerberos auth error krb5kdc_err_c_principal_unknown (6)

Hi,

I'm trying to setup my alfresco services to authenticate users against our AD (MS 2008R2SP1 domain controller).

The AD service account is configured this way:

  dn: CN=AlfrescoHTTP,OU=USERS,OU=COMMON,DC=MYDOMAIN,DC=LOCAL
  changetype: add
  userAccountControl: 4784640
  sAMAccountName: AlfrescoHTTP
  userPrincipalName: HTTP/alfrescoserver.mydomain.local@MYDOMAIN.LOCAL
  servicePrincipalName: HTTP/alfrescoserver.mydomain.local
  servicePrincipalName: HTTP/alfrescoserver

From the alfresco server, I'm testing authentication using kinit tool:
 > kinit -V HTTP/alfrescoserver.mydomain.local
  I got following error: "Client not found in Kerberos database while getting initial credentials"
  (authentication using kinit is working fine for a regular MSAD account)
   
I made network captures, and see that a Kerberos AS-REQ is send to the domain controller with following parameters
   Client Name (Principal): HTTP/alfrescoserver.mydomain.local
     Name-type: Principal (1)
     Name: HTTP
     Name: alfrescoserver.mydomain.local
     Realm: MYDOMAIN.LOCAL
   Server Name (Service and Instance): krbtgt/MYDOMAIN.LOCAL
     Name-type: Service and Instance (2)
     Name: krbtgt
     Name: MYDOMAIN.LOCAL
Server response is:
  Kerberos BRK-ERROR
 Pvno: 5
 MSG Type: KRB-ERROR (30)
 error_code: KRB5KDC_ERR_C_PRINCIPAL_UNKNOWN (6)

But the Client Principal name is matching the UPN of the service account.....
Please help.

Thanks,

Vincent