Multiple requests for the default Dial Plan failed because a default is not defined. At least %1 different users have requested ...

Multiple requests for the default Dial Plan failed because a default is not defined.

At least %1 different users have requested an unknown Dial Plan in the last hour. This may represent an issue that is not specific to individual users. This message will not be repeated again for %2 hours even though the problem may persist.
Cause: Lync Server clients that are enabled for Unified Communications may request the details of a specific Dial Plan based on group policy settings or based on user selection.
Resolution:
Review group policy settings and ensure the specified Dial Plans are defined in the system.