Important update available for Exchange Server 2013 hybrid deployments
An important update is now available to resolve issues customers are currently experiencing when using the Hybrid Configuration Wizard (HCW) to create a new or manage an existing hybrid deployment with Microsoft Exchange Server 2013.
If you currently have an Exchange 2013-based hybrid deployment configured, you will not notice any issues unless you rerun the HCW as part of updating or managing your existing hybrid features. Unless you need to reconfigure your hybrid deployment, you can simply wait for the next update of Exchange Server 2013 (Cumulative Update 6) to correct this issue with the HCW.
Read more at source: http://blogs.technet.com/b/exchange/archive/2014/07/30/important-update-available-for-exchange-server-2013-hybrid-deployments.aspx