Error 18015 Autocad ((link)) -

Overly aggressive real-time scanning can lock temporary files that AutoCAD is trying to read, leading to an access violation.

AutoCAD uses a service (FlexNet or the newer AdskLicensing service) to manage the "handshake" with Autodesk’s servers. Over time, the files that store your login credentials and machine ID can become corrupted. If AutoCAD tries to read a corrupted file during startup, it triggers Error 18015 to prevent unauthorized usage. error 18015 autocad

Enterprise-level antivirus software or aggressive firewalls often view the licensing verification process as "suspicious network activity." If your firewall blocks the AdskLicensingService.exe executable, AutoCAD cannot validate your license, resulting in a timeout that presents as Error 18015. AutoCAD cannot validate your license