The FLEXlm license manager is extremely sensitive to time discrepancies. If your clock is off by even 5 minutes, Error 20 can appear.
When you launch AutoCAD, it sends a request to the license server, asking to "check out" a seat. If the server has available seats and can verify your permissions, it grants the license, and the software opens. 20 generic license checkout error autocad
Autodesk products are forward-compatible but not always backward-compatible in the way they request licenses. If you have a license file for AutoCAD 2022, but you are trying to run AutoCAD 2024, the older license file may not recognize the request from the newer software. The FLEXlm license manager is extremely sensitive to
C:\Program Files (x86)\Common Files\Autodesk Shared\AdskLicensing folder. He ran the uninstall.exe it grants the license