Just out of interest, I checked for AutoAuthSetup() on mediawiki.org. I found this:
http://www.mediawiki.org/wiki/Manual:Hooks/AutoAuthenticate
"[image: Warning]http://www.mediawiki.org/wiki/Image:Attention_niels_e pting.svg *Warning*: This hook doesn't exist anymore in 1.13 or above, use UserLoadFromSessionhttp://www.mediawiki.org/wiki/Manual:Hooks /UserLoadFromSessioninstead."
Maybe the Ldap extension doesn't work correctly with 1.13.1?
The auto-authentication hook changed to something else in 1.13. The version of the plugin from SVN, which is fairly stable, but isn't officially released, works with 1.13+, and should work with earlier versions fine as well.
V/r,
Ryan Lane