I just ran into a strange thing, having an account with a distinguished name looking like : CN=LLAMOSI\, Faust, OU=XXXX,DC=mydomain,dc=local:
The mistake come from the full name which has a ",". Only the Display name may have it.
You cannot edit the distinguished name attribute with adsiedit.msc, because it is owned by "SYSTEM".
Thanks to Brandon Aiken for hitting the coma on the ActiveDir mailing list