By default, each sub-user has its own private storage (\My Storage\ ). A sub-user cannot access other sub-user's folder, unless the folder is shared to him. ( The group owner / group admin users can access other group members' folders. )
So if you are the group owner (or group admin), then by default, sub-users cannot access your folders. You must share a folder to the sub-user or to the whole group. Please make sure to set the permission to "View Original Only" (same as "download-only", or "read-only"). Your sub-users can logon and access your shared folders from their "\DriveHQ Share\" virtual folder.