Symptoms
You can’t leave a voicemail until the Skype for Business Front-End service gets restarted in a Microsoft Skype for Business Server 2015 environment.
In addition, the following events are logged on the Skype for Business Server 2015, Front End server:
Log Name: Lync Server Source: LS Exchange Unified Messaging Routing Date: DATE/TIME Event ID: 44005 Task Category: LS Exchange Unified Messaging Routing Level: Error Keywords: Classic User: N/A Computer: SERVER Description:
Unexpected exception occurred in the Exchange Unified Messaging Routing Application. Exception: System.DirectoryServices.ActiveDirectory.ActiveDirectoryServerDownException: The RPC server is unavailable. Name: "server.domain.com" at System.DirectoryServices.ActiveDirectory.Forest.GetTrustsHelper(String targetForestName) at Microsoft.Rtc.Internal.ExumDialPlanData.GetTrustedForests() at Microsoft.Rtc.Internal.ExumDialPlanData.RefreshDomainDictionary()
Log Name: Lync Server Source: LS Exchange Unified Messaging Routing Date: DATE/TIME Event ID: 44005 Task Category: LS Exchange Unified Messaging Routing Level: Error Keywords: Classic User: N/A Computer: SERVER Description:
Unexpected exception occurred in the Exchange Unified Messaging Routing Application. Exception: System.NullReferenceException: Object reference not set to an instance of an object. at Microsoft.Rtc.Internal.Domain.GetHashCode() at System.Collections.Generic.ObjectEqualityComparer`1.GetHashCode(T obj) at System.Collections.Generic.Dictionary`2.Insert(TKey key, TValue value, Boolean add) at Microsoft.Rtc.Internal.ExumDialPlanData.RefreshDomainDictionary() at Microsoft.Rtc.Internal.ExumDialPlanData.TimerElapsedEventHandler(Object sender, ElapsedEventArgs args)
Log Name: Lync Server Source: LS Exchange Unified Messaging Routing Date: DATE/TIME Event ID: 44008 Task Category: LS Exchange Unified Messaging Routing Level: Error Keywords: Classic User: N/A Computer: SERVER Description: Dial Plan Unknown Dialplan [DIALPLAN.domain.com] is not recognized by routing application Cause: Dial plan does not exist, or Microsoft Skype for Business 2015 does not have permission to read the relevant Active Directory objects.
Cause
This issue occurs because the Skype for Business Front-End service cannot connect to Domain Controller to read dial plan records.
Resolution
To fix this issue, install the May 2017 cumulative update 6.0.9319.281 for Skype for Business Server 2015, Front End server and Edge server.
