The source for the LDAPAuthenticator is the place to start in understanding how jForum will validate against LDAP. Here you can see how the configuration properties get converted into LDAP lookup info (e.g. LDAP DN strings).
Note: anything that looks like:
SystemGlobals.getValue(ConfigKeys.X_Y_Z))
is getting the configuration setting for x.y.z. E.g. the ldap.login.prefix setting.
If I'm reading the code and error correctly, the code assumes that if the generated lookupPrincipal does not exist, a NamingException will be thrown by
Java's Directory code. But this does not seem to be happening on your set up.
This could be due to a configuration issue or it could be due to a version difference in your version of the directory code.
The only way to really track this down is to play around with the code to find out. E.g. replace line 124 which reads:
with something like:
[originally posted on jforum.net by monroe]