I am in initial testing taking an ArcGIS Organization Portal web map offline using collector. To keep it simply, there is only one feature service (with one layer) wihin the map, offline mode is enabled, layer is in edit mode and web map has appropriate offline-ready tag.
Map appears and I am able to open it within Collector. I can click the Download cloud and choose area and detail but when starting the download process I am hit with the error message: Map Download Failed...Unable to download the map...Empty username/password.
Portal is set up with Active Directory and using a VPN client to access via iPhone 5s (iOS 7.1.1).
I was successful in testing connected environment including editing.