Mission Maker v 1.6 (Non Auto-Updater) version will be avaliable to download here. Link: ModDB Link - Auto Updater will work on the latest releases so don't worry, auto-updater here is not disabled it's just a current version of the software, but for people that have problems in general with auto-updater feature from v 1.5 and can't update from v 1.5 version onwards.
Also, new v 1.6 mission has been released - that's starting a new Mission Pack. It has been made by Benjamin and it's called: Night Of Dead
Download under the video description!