Error "...valid username and password" trying to connect Sugar to SBS 2003 Domain

[comas17]

Hi all
I'm trying to configure SugarCRM to use LDAP Authentication with my Windows Small Business Server 2003 Domain but I receive a "strange" error

Active Directory Domain based on Windows Small Business Server 2003 SP2

SugarCRM 5.1.0b Connunity Edition
Installed on Windows 2003 Server Web Edition (domain member server)
Database MySQL 5.0.45

Here's my settings
My domain name is "my_domain_name.corp"

Enable LDAP . YES
Server: server_name (domain controller name)
Port Number: 389
Base DN: DC=my_domain_name,DC=corp
Bind Attribute: userPrincipalName
Login Attribute: sAMAccountName
Authenticated User: domain_user@my_domain_name.corp
Authenticated Password: domain_user_password
Auto Create Users: YES
Encryption Key: empty

I'm trying to login using this syntax
User Name = user@my_domain_name.corp
Password = **********

Error: You must specify a valid username and password.

?????? I'm absolutely sure that username and password are correct...

Any idea ?
Thank you

Corrado

[comas17]

Any idea ?

I know that it could seem only a wrong username and/or wrong password but I tried many different users and the error is always the same.

I'm not sure that settings are correct; does anybody can tell me if they are correct ?

Which is the correct syntax for username: "domain\user" or "user@domain" ?

Thank you

Corrado