System failed to generate offline data

I'm having no luck trying to generate an offline bundle. I get the below response after clicking the Generate Offline Bundle button:

System failed to generate offline data.

Error downloading feature service.and Stack Trace is: at Geocortex.Essentials.Html5Viewer.Management.Offline.ResourceAggregator.Model.BundleCatalogEntry.AddMapServiceRelations(Uri serviceUri, String token) at Geocortex.Essentials.Html5Viewer.Management.Offline.ResourceAggregator.Model.BundleCatalogEntry.AddMapResource(MapServiceBaseConfig resource, String uriString, Boolean isFeatureService, String token) at Geocortex.Essentials.Html5Viewer.Management.Areas.Html5Viewer.Controllers.OfflineController.HandleMapRequests(IdentifiableResourceCollection`1 mapServices, ManifestEntry offlineManifest, ConfigModel manifestConfigParams, String[] baseMapIdList, String[] baseMapFilenameList)

The remote server returned an error: (401) Unauthorized.and Stack Trace is: at System.Net.HttpWebRequest.GetResponse() at Geocortex.Essentials.Html5Viewer.Management.Offline.ResourceAggregator.Model.BundleCatalogEntry.AddMapServiceRelations(Uri serviceUri, String token) 

Any help or suggestions would be greatly appreciated.

Regards,

Elliott