NAV 2013 NAS File Import Call back Error

Dear Experts

I’m trying import txt file using NAS. NAS throws the Call back error while using the standard SlientUpload function. I have tried in RTC Client for importing the file, NAV repeatedly asked confirmation dialog to access the File every time in a new NAV session. I have overcome the confirmation dialog using the “ServicePrincipalNameRequired” = true in the user ClientUserSetting. After this setting it stopped asking confirmation in RTC Client. But It seems the same confirmation is comes in the NAS too. This was reason for error in the NAS Import. I have tried to create SPN for the Domin user. Any special setup is required in Config file for this? Any suggestion is highly appreciated.

The below message for Event Log

The Microsoft Dynamics NAV Application Server session has failed. Reason: Type: Microsoft.Dynamics.Nav.Types.Exceptions.NavNCLCallbackNotAllowedException
SuppressMessage: False
FatalityScope: None
Message: Microsoft Dynamics NAV Application Server attempted to issue a client callback to create a DotNet object: System.IO.File (CodeUnit 419 File Management). Client callbacks are not supported on Microsoft Dynamics NAV Application Server.
StackTrace:
at Microsoft.Dynamics.Nav.Runtime.HeadlessClientCallback.CreateDotNetHandle(String assemblyFullName, String typeName, Guid formHandle, String varName, Boolean createInstance, Object[] arguments)
at Microsoft.Dynamics.Nav.Runtime.NavDotNet.CheckTypeIsLoaded()
at Microsoft.Dynamics.Nav.Runtime.NavDotNet.InvokeStaticMethod[T](String methodName, UInt32 methodIndex, Object[] arguments)
at Microsoft.Dynamics.Nav.BusinessApplication.Codeunit419.UploadFileSilent_Scope.OnRun()
at Filter.InvokeWithFilter(NavMethodScope )
at Microsoft.Dynamics.Nav.BusinessApplication.Codeunit419.UploadFileSilent(NavText clientFilePath)
at Microsoft.Dynamics.Nav.BusinessApplication.Codeunit419.OnInvoke(Int32 memberId, Object[] args)
at Microsoft.Dynamics.Nav.BusinessApplication.Codeunit58141.OnRun_Scope.OnRun()
at Filter.InvokeWithFilter(NavMethodScope )
at Microsoft.Dynamics.Nav.BusinessApplication.Codeunit58141.OnRun(INavRecordHandle εrec)
at Microsoft.Dynamics.Nav.Runtime.NavCodeunit.DoRun(DataError errorLevel, NavRecord record)
at Microsoft.Dynamics.Nav.BusinessApplication.Codeunit59000.OnRun_Scope.OnRun()
at Filter.InvokeWithFilter(NavMethodScope )
at Microsoft.Dynamics.Nav.BusinessApplication.Codeunit59000.OnRun(INavRecordHandle εrec)
at Microsoft.Dynamics.Nav.Runtime.NavCodeunit.DoRun(DataError errorLevel, NavRecord record)
at Microsoft.Dynamics.Nav.Runtime.NavCodeunit.InvokeRun(Int32 objectId, Object[] args)
at Microsoft.Dynamics.Nav.Runtime.NavApplicationServer.InternalStartNas(Object config)
Source: Microsoft.Dynamics.Nav.Ncl
HResult: -2146233088

Thanks in advance