The migration to a 123D log-in has caused some unforeseen issues for most users. As we get them sorted out, we're posting the solutions here.
A lot of users are unable to log in to their accounts since the migration to Autodesk 123D and the problem has usually been a matter of Case-Sensitivity or remembering that the new password has numbers AND letters. Autodesk log in required you to create a password with at least one letter and a number - be sure you remember to copy exactly!
Thanks for your patience as we continue #fixingtinkercad, and as always, email us at Team@Tinkercad.com with any questions.