Any ideas about a potential fix? I managed to get the error trace log (see below).
# CRM Tracing Version 2.0
# LocalTime: 2016-06-29 14:15:01.534
# Categories: *:Error
# CallStackOn: Yes
# ComputerName: MAINCPU
# CRMVersion: 8.1.0.359
[2016-06-29 14:15:01.534] Process:OUTLOOK |Organization:fffe3699-21ad-498f-8328-bc3920573625 |Thread: 26 |Category: Application.Outlook |User: 00000000-0000-0000-0000-000000000000 |Level: Error |ReqId: 00000000-0000-0000-0000-000000000000 | CrmServiceForOutlook.Execute ilOffset = 0x7
at CrmServiceForOutlook.Execute(OrganizationRequest request, Boolean wrapException) ilOffset = 0x7
at EmailForOutlook.Microsoft.Crm.Application.SMWrappers.IEmailForOutlook.DeliverPromote(String messageId, String subject, String from, String to, String cc, String bcc, Double receivedon, String submittedBy, String importance, String body, IDynamicEntityCollectionForOutlook attachments, Int32 attachmentCount, IDynamicEntityForOutlook extraProperties, String entityXml, String regardingId, Int64 regardingObjectType, String crmId, Int32& notification) ilOffset = 0x1C7
>FaultExceptionDetails: Unhandled Exception: System.ServiceModel.FaultException`1[[Microsoft.Xrm.Sdk.OrganizationServiceFault, Microsoft.Xrm.Sdk, Version=8.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35]]: Cannot insert duplicate key.Detail:
<OrganizationServiceFault xmlns:i="www.w3.org/.../XMLSchema-instance" xmlns="schemas.microsoft.com/.../Contracts">
<ErrorCode>-2147220937</ErrorCode>
<ErrorDetails xmlns:d2p1="schemas.datacontract.org/.../System.Collections.Generic" />
<Message>Cannot insert duplicate key.</Message>
<Timestamp>2016-06-29T04:15:01.1686786Z</Timestamp>
<InnerFault>
<ErrorCode>-2147220937</ErrorCode>
<ErrorDetails xmlns:d3p1="schemas.datacontract.org/.../System.Collections.Generic" />
<Message>Cannot insert duplicate key.</Message>
<Timestamp>2016-06-29T04:15:01.1686786Z</Timestamp>
<InnerFault>
<ErrorCode>-2147220937</ErrorCode>
<ErrorDetails xmlns:d4p1="schemas.datacontract.org/.../System.Collections.Generic" />
<Message>Cannot insert duplicate key.</Message>
<Timestamp>2016-06-29T04:15:01.1686786Z</Timestamp>
<InnerFault i:nil="true" />
<TraceText i:nil="true" />
</InnerFault>
<TraceText i:nil="true" />
</InnerFault>
<TraceText i:nil="true" />
</OrganizationServiceFault>
Server stack trace:
at System.ServiceModel.Channels.ServiceChannel.HandleReply(ProxyOperationRuntime operation, ProxyRpc& rpc)
at System.ServiceModel.Channels.ServiceChannel.Call(String action, Boolean oneway, ProxyOperationRuntime operation, Object[] ins, Object[] outs, TimeSpan timeout)
at System.ServiceModel.Channels.ServiceChannelProxy.InvokeService(IMethodCallMessage methodCall, ProxyOperationRuntime operation)
at System.ServiceModel.Channels.ServiceChannelProxy.Invoke(IMessage message)
Exception rethrown at [0]:
at System.Runtime.Remoting.Proxies.RealProxy.HandleReturnMessage(IMessage reqMsg, IMessage retMsg)
at System.Runtime.Remoting.Proxies.RealProxy.PrivateInvoke(MessageData& msgData, Int32 type)
at Microsoft.Xrm.Sdk.IOrganizationService.Execute(OrganizationRequest request)
at Microsoft.Xrm.Sdk.Client.OrganizationServiceProxy.ExecuteCore(OrganizationRequest request)
at Microsoft.Crm.Application.SMWrappers.ClientOrganizationServiceProxyBase.Execute(OrganizationRequest request)
at Microsoft.Crm.Application.SMWrappers.CrmServiceForOutlook.Execute(OrganizationRequest request, Boolean wrapException)
[2016-06-29 14:15:01.556] Process:OUTLOOK |Organization:fffe3699-21ad-498f-8328-bc3920573625 |Thread: 26 |Category: Application.Outlook |User: 00000000-0000-0000-0000-000000000000 |Level: Error |ReqId: 00000000-0000-0000-0000-000000000000 | ilOffset = 0xFFFFFFFF
> TraceException: Unhandled Exception: System.Runtime.InteropServices.COMException: Cannot insert duplicate key.
at Microsoft.Crm.Application.SMWrappers.CrmServiceForOutlook.Execute(OrganizationRequest request, Boolean wrapException)
at Microsoft.Crm.Application.SMWrappers.EmailForOutlook.Microsoft.Crm.Application.SMWrappers.IEmailForOutlook.DeliverPromote(String messageId, String subject, String from, String to, String cc, String bcc, Double receivedon, String submittedBy, String importance, String body, IDynamicEntityCollectionForOutlook attachments, Int32 attachmentCount, IDynamicEntityForOutlook extraProperties, String entityXml, String regardingId, Int64 regardingObjectType, String crmId, Int32& notification)