Document Viewer Error : cache has not been setup

<add key="lt.Cache.Directory" value="C:\Development\Assets\Cache"/>
  <add key="lt.Cache.VirtualDirectory" value="http://core/_cache"/>

var loadOptions = new LoadDocumentOptions();
            loadOptions.UseCache = true;
            loadOptions.CachePolicy = ServiceHelper.CreatePolicy();
            loadOptions.WebClient = null; 
            
            
            if (request.Options != null)
            {
                loadOptions.AnnotationsUri = request.Options.AnnotationsUri;
                loadOptions.Name = request.Options.Name;
                loadOptions.Password = request.Options.Password;
                loadOptions.LoadEmbeddedAnnotations = request.Options.LoadEmbeddedAnnotations;
                loadOptions.MaximumImagePixelSize = request.Options.MaximumImagePixelSize;
            }
            var documentName = request.Uri.ToString();

            //Check if this document was uploaded, then hope the user has set LoadDocumentOptions.Name to the original file name
            if (DocumentFactory.IsUploadDocumentUri(request.Uri) && !string.IsNullOrEmpty(loadOptions.Name))
            {
                // Use that instead
                documentName = loadOptions.Name;
            }

            var originalSetting = DocumentConverterPreferences.TryEnableTextFilter(DocumentFactory.RasterCodecsTemplate, documentName);
            try
            {
                Document document = null;
                try
                {
                    // first, check if this is pre-cached
                    if (PreCacheHelper.PreCacheExists)
                    {
                        string documentId = PreCacheHelper.CheckDocument(request.Uri, loadOptions.MaximumImagePixelSize);
                        if (documentId != null)
                            document = DocumentFactory.LoadFromCache(documentId);
                    }
                    if (document == null)
                    {
                        document = DocumentFactory.LoadFromUri(request.Uri, loadOptions);
                        if (document == null)
                            throw new InvalidOperationException("Failed to load URI: " + request.Uri);
                        ServiceHelper.SetRasterCodecsOptions(document.RasterCodecs, request.Resolution);
                        document.AutoDeleteFromCache = false;
                        document.AutoSaveToCache = false;
                        document.SaveToCache(); // The exception is thrown at this line
                    }
                    return new LoadFromUriResponse { Document = document };
                }
                finally
                {
                    if (document != null)
                        document.Dispose();
                }
            }
            finally
            {
                DocumentConverterPreferences.RestoreTextFilter(DocumentFactory.RasterCodecsTemplate, originalSetting);
            }