I had a similar thing today as well. I amended some records on FTM for Mac and I got the message that I needed to sign in. I never get that message. Anyway I signed in and it didn't accept my details which I know were correctly entered. Later on it worked and then I tried to sync and it failed. It has been working well for months. I must assume that Ancestry were doing some maintenance and they got it wrong. I must assume that rkj827 and I are not alone with this issue.