Error on add section to workplace

Hi everyone,

i wanna ask you about this error below. I can't add section on the workplace and that error is showing like this.

The server encountered an error processing the request. The exception message is 'Sequence contains no matching element'. See server logs for more details. The exception stack trace is:
 
at System.Linq.Enumerable.First[TSource](IEnumerable`1 source, Func`2 predicate) at Terrasoft.Configuration.Section.SectionRepository.Get(Guid sectionId) at Terrasoft.Configuration.Workplace.WorkplaceManager.AddSectionToWorkplace(Guid workplaceId, Guid sectionId) at SyncInvokeAddSectionToWorkplace(Object , Object[] , Object[] ) at System.ServiceModel.Dispatcher.SyncMethodInvoker.Invoke(Object instance, Object[] inputs, Object[]& outputs) at System.ServiceModel.Dispatcher.DispatchOperationRuntime.InvokeBegin(MessageRpc& rpc) at System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage5(MessageRpc& rpc) at System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage11(MessageRpc& rpc) at System.ServiceModel.Dispatcher.MessageRpc.Process(Boolean isOperationContextSet)