Recently I came across this error whilst troubleshooting a failing AutoCAD 2021 install on a Windows 7 desktop that had a recent Windows Update applied. Initially, upon starting AutoCAD the error reported as the (unfortunately) common - Out Of Time error message;
But following the best practices outlined within this Autodesk article still failed to remedy the issue. So a clean uninstall of all Autodesk apps was undertaken, including removal of licensing modules, residual install folders and Windows registry keys. Upon re-install and updating of the Autodesk 2021 product, we were then greeted with a new, slightly unique error;
The License manager is not functioning or improperly installed.
AutoCAD LT will shut down now.
Eventually it was discovered that Autodesk Licensing Certificates were missing and needing to be manually downloaded and installed (MSI file link below);
(Note that if this link fails or opens in the browser, you may need to use the "Save As" option, then check the file extension of the installer is a .MSI file).
Upon installing the updated Autodesk certificates, then logging back in as the user via their Autodesk Desktop App, AutoCAD loaded and worked as expected without further error.