Map: NAV Customer Card to Account

Running the default connector map "NAV Customer Card to Account", results in "Exception occurred in Microsoft Dynamics NAV". Checking the application logs reveals the following errors:

Exception occurred in Microsoft Dynamics NAV
    --- Exception Dump ---
    Caught Exception: [Microsoft.Dynamics.Integration.AdapterAbstractionLayer.AdapterException] Exception occurred in Microsoft Dynamics NAV
    Stack trace:
   at Microsoft.Dynamics.Integration.Adapters.Nav2009.NavObjectProvider.ReadObjectKeys(DateTime modifiedDate)
   at Microsoft.Dynamics.Integration.Service.Tasks.MapWork.ReadObjectKeyList(DbMap map, DateTime queryDate, Int32& count)
   at Microsoft.Dynamics.Integration.Service.Tasks.MapWork.ProcessRecordsImplementation(OperationType operationType)

    Inner Exception: [System.NullReferenceException] Object reference not set to an instance of an object.
    Stack trace:
   at Microsoft.Dynamics.Integration.Adapters.Nav2009.CustomerObjectProvider.ReadDynamicObjectKeys(DateTime modifiedDate)
   at Microsoft.Dynamics.Integration.Adapters.Nav2009.NavObjectProvider.ReadObjectKeys(DateTime modifiedDate)

Any ideas on how to troubleshoot this further? Other maps complete without errors.

Regards

Charlie