Thread:Extension talk:LDAP Authentication/Failed to bind user/reply

It's possible that your Active Directory server does not allow unencrypted binds. You should try to search against the directory server manually using ldapsearch (or, if you are using Windows, the Windows equivalent), ensuring you are binding unencrypted there too.

I really recommend trying to get this working with SSL, though, as it is more secure. There are instructions for doing so in the Requirements portion of the documentation.