You can set this flag. See my web page for a description of the bits of the flag and what they mean.
http://home.comcast.net/~habullock/Win32Admin.htm#User
Did you read the rest of the this thread? There is posted code that works using the WinNT:// ADSI provider.
UserAccountControl would be used for LDAP and should also work. My guess is that you are not viewing the the same server with ADSIEDIT that you had changed.
