Outlook Address Book is freezing

Hello,<o:p></o:p>

I have mixed Exchange 2010 and 2013 environment with
couple of users migrated to Exchange 2013. For migrated users the Address Book
is freezing very often, usually at the start or after long time of inactivity.
The message is "Outlook is trying to retrieve data from the Microsoft
Exchange server.." The Address book is opened after several minutes. Other
features like sending / receiving emails, calendar, and tasks are working.
During this time when Address Book is "thinking" :) the Directory
type Connection Status is Disconnecting<o:p></o:p>

Thank you for your support.

Br

Csaba Papp