Update: It's not Microsoft, and it's not us. Here is what MacKiev says
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TreeSync stopped working
Your trees cannot be synced at present because on March 29, 2017, Ancestry permanently retired TreeSync®. It is being replaced by Software MacKiev's state-of-the-art FamilySync syncing technology. FamilySync will be available only
in our Family Tree Maker 2017 edition when it is released.
Please note that it is only syncing that is not working. As agreed with Ancestry, hints, search, merge, maps, Web view and other connections to Ancestry will all continue running in older versions until FTM 2017 is released. We hope that this will allow you
to continue your research while waiting for syncing to resume.
FTM 2017 is currently undergoing thorough testing to ensure that the released product works exactly as it should. You can follow the latest news on the release
here.
If you would like to find out about purchasing or upgrading to FTM 2017, product features and syncing, or the upcoming release, please click
here to read our FAQ where we provide answers to your questions.