Error: Access Denied - How can update user attribute ?

Error: Access Denied - How can update user attribute ?

Hi there,
I've recently installed ADManager Plus and have been trying its features around.
I need to change many attributes of users account already present in AD.
I try using a csv file, a list of users with this attribute:
givenName
sn
telephoneNumber
mail
userPrincipalName
physicalDeliveryOfficeName
title
company
department
postalCode
homeDrive
homeDirectory

It works with some users, while most of the others does not work, with this error:
Unable to retrieve the object from AD - The object does not exist or access denied

Am I missing something in the configuration?

Thank you!
              New to ADManager Plus?

                New to ADSelfService Plus?