I have recently become an administrator for a OF 3.6.4 system and switched to LDAP a few days ago.
Everything went very smoothly and 99% of users are happy.
I have got a few users unable to log on.
I have searched the interwebs and found the followig things that may be causing problems:
Special characters in the password - #,^,&, space, etc. I had the user only use a full stop and no go.
Login name in capitals in AD - not true
Log on to restriction on AD - not true
The user stil get an error stating that the user is either unknown on the server, already logged on or something like that. Logs show Plain user authentication failed and nothing else.