Recurring appointments - An unknown error occurred while synchronizing data to Outlook

We are running CRM 2012 UR6 with outlook 2010 and using CRM Outlook client.

Some of our users experiencing strange issues with their recurring appointments. They keep getting sync error even when new recurring appointments are created from Outlook. The appointments get created in CRM but always present an error on a sync.

This is the trace log:

at ResourceForOutlook.Microsoft.Crm.Application.SMWrappers.IResourceForOutlook.GetString(Int32 id)

at ThreadsSupport.ExecuteThreadProc(ThreadProc threadProc, IntPtr parameter)

> Exception: System.Runtime.InteropServices.COMException (0x80040203): Resource not found(-2146233033).

at Microsoft.Crm.Application.SMWrappers.ResourceForOutlook.Microsoft.Crm.Application.SMWrappers.IResourceForOutlook.GetString(Int32 id)

More ....

at RuntimeMethodHandle._InvokeMethodFast(IRuntimeMethodInfo method, Object target, Object[] arguments, SignatureStruct& sig, MethodAttributes methodAttributes, RuntimeType typeOwner)

at RuntimeMethodHandle.InvokeMethodFast(IRuntimeMethodInfo method, Object target, Object[] arguments, Signature sig, MethodAttributes methodAttributes, RuntimeType typeOwner)

at RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture, Boolean skipVisibilityChecks)

at Delegate.DynamicInvokeImpl(Object[] args)

at Control.InvokeMarshaledCallbackDo(ThreadMethodEntry tme)

at Control.InvokeMarshaledCallbackHelper(Object obj)

at ExecutionContext.runTryCode(Object userData)

at RuntimeHelpers.ExecuteCodeWithGuaranteedCleanup(TryCode code, CleanupCode backoutCode, Object userData)

at ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state)

at ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean ignoreSyncCtx)

at ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)

at Control.InvokeMarshaledCallback(ThreadMethodEntry tme)

at Control.InvokeMarshaledCallbacks()

at Control.WndProc(Message& m)

at ScrollableControl.WndProc(Message& m)

at Form.WndProc(Message& m)

at ControlNativeWindow.OnMessage(Message& m)

at ControlNativeWindow.WndProc(Message& m)

at NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)

at UnsafeNativeMethods.DispatchMessageW(MSG& msg)

at ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(IntPtr dwComponentID, Int32 reason, Int32 pvLoopData)

at ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context)

at ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context)

at Application.RunDialog(Form form)

at Form.ShowDialog(IWin32Window owner)

at Form.ShowDialog()

at OutlookUIHelper.ShowDialog(Form form)

at DownloadStatus.RunUserInterfaceThread()

at ThreadHelper.ThreadStart_Context(Object state)

at ExecutionContext.runTryCode(Object userData)

at RuntimeHelpers.ExecuteCodeWithGuaranteedCleanup(TryCode code, CleanupCode backoutCode, Object userData)

at ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state)

at ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean ignoreSyncCtx)

at ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)

at ThreadHelper.ThreadStart()

>crm id :'{AD0FD54F-9FB6-E111-B1C5-0050568F12FB}', Error:An unknown error occurred while synchronizing data to Outlook.

I also see this in the log

at OutlookItemWrapper.get_EntityTypeCode()

at AppointmentItemWrapper.get_EntityTypeCode()

at TrackInCrmRegion.AddRegardingRow(OutlookItemWrapper item)

at TrackInCrmRegion.CreateRecipientUI(OutlookItemWrapper item)

at TrackInCrmRegion.CreateUI()

at TrackInCrmRegion.<UpdateUI>b__0()

at ExceptionFilter.TryFilterAllCatch(Action body, Action`1 filter)

at TrackInCrmRegion.UpdateUI()

at <>c__DisplayClass1.<UpdateFormRegionUI>b__0()

at <>c__DisplayClassb.<InvokeSafe>b__9()

at ExceptionFilter.TryFilterAllCatch(Action body, Action`1 filter)

at <>c__DisplayClassb.<InvokeSafe>b__8()

at RuntimeMethodHandle._InvokeMethodFast(IRuntimeMethodInfo method, Object target, Object[] arguments, SignatureStruct& sig, MethodAttributes methodAttributes, RuntimeType typeOwner)

at RuntimeMethodHandle.InvokeMethodFast(IRuntimeMethodInfo method, Object target, Object[] arguments, Signature sig, MethodAttributes methodAttributes, RuntimeType typeOwner)

at RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture, Boolean skipVisibilityChecks)

at Delegate.DynamicInvokeImpl(Object[] args)

at Control.InvokeMarshaledCallbackDo(ThreadMethodEntry tme)

at Control.InvokeMarshaledCallbackHelper(Object obj)

at Control.InvokeMarshaledCallback(ThreadMethodEntry tme)

at Control.InvokeMarshaledCallbacks()

at Control.MarshaledInvoke(Control caller, Delegate method, Object[] args, Boolean synchronous)

at Control.Invoke(Delegate method, Object[] args)

at Control.Invoke(Delegate method)

at OutlookInstanceCache.InvokeSafe(Control control, Action method, Func`1 parentWindow)

at CrmManagedRegion.UpdateFormRegionUI(String searchKey)

at <>c__DisplayClass97.<UpdateFormRegionUI>b__94()

at ExceptionFilter.TryFilterAllNoCatch(Action body, Action`1 filter)

at OutlookInstance.UpdateFormRegionUI(String searchKey)

>UserProperties collection doesn't contain all MAPI properties for item: Northline Meeting

Any ideas what else to check?