Some users are not synchronized from AD to OID (11g) with DIP

Hi Everybody,

i have already installed OID 11g and started synchronization from AD to OID with DIP.
As a result i see that some of the users are not synchronized from  AD to OID.
I could not understand why some users are not synched ? Where should i start to investigate ?

Note: after some search on AD side i see that "some synchronized user and not synchronized user are at the same tree level"

best regards