When setting up LDAP authentication, there needs to be a valid user name in the user field and that accounts password into Password. The user has to be in the correct format in the field to work correctly.
Ldap authentication can be done with any account that has read access to the ldap database. This can be any normal user account, by default.
Best practice is to use a service account that has password set to never expire. If a normal user account is used here, if the password changes, the ldap authentication will fail. Also, the ldap server may lock that particular account out network wide, per the domain's policy.
The user name has to be in the correct format. Often, the account will have the same name for all the options, but this depends on how the users are set up and is not a given. However, it is easy to find what name and how to format it in the user field, by looking in Active Directory (other directory services that support ldap will also authenticate, however, this article is focused on finding the information in AD).
From Active Directory Users and Computers, rich click on the user object and choose Properties..
On General tab
Display name -
What is displayed as display name, usually first and last name. This depends on how this attribute is set in AD.
e.g. - Kace.admin
On Account Tab -
User logon name (userprincipalname:) -
e.g. - firstname.lastname@example.org
user logon name (pre-Windows 2000) -
e.g. - domain\user_name