Originally published and re-distributed upon request at:http://blogs.msdn.com/scottos/archive/2008/12/05/office-communicator-clients-cannot-communicate-with-contacts-homed-on-yahoo-messenger-network.aspx

Yahoo! will be undergoing an emergency maintenance from 4:30pm to 4:30am PST. During this period, users will see intermittent presence issues. All other functionality will not be impacted.

More Information:

After the maintenance window expires, if you find you are still having issues, please first log out & then back into your Communicator client. If the issue still reproduces/occurs for you, please restart Edge Front-End services first. Allow me to apologize for this up front; I understand this will require an “emergency service restart change request” for some of you. If all this fails to resolve the PIC issue between your LCS/OCS deployment and Yahoo!, please engage Microsoft Customer Support Services. Premier customers: please leverage your Technical Account Manager to initiate the case creation process. Please be prepared to supply Edge Server logs, remote access via our EasyAssist applications from MSFT, and we will do our best to investigate and resolve this in a timely manner.

or those that subscribe to the Public Internet Connector (PIC) feature in Office Communication Server, a recent change at AOL may impact you. As with all communication to and from OCS, certificates are used to encrypt and authenticate traffic. The PKI infrastructure AOL utilized in the past has changed and they have moved to their new AOL root certificates. Because of this, the OCS Edge/Access Proxy servers will not be able to validate any AOL traffic without a root certificate update.

The official notice may be found here:http://blogs.msdn.com/scottos/archive/2008/12/02/office-communicator-clients-cannot-communicate-with-contacts-homed-on-aol.aspx

A link to the AOL certificates may be found directly here: https://pki-info.aol.com/AOL/

Remember. only the edge servers (those authenticating traffic) require the updates - not your clients - and a restart/reboot is not required