This error message may occur if you are using BitDefender Antivirus program.
- Launch BitDefender Antivirus.
- Click on "Options" at the top right menu and select "Expert View".
- Open the Antivirus section. In "Shield" tab, click on the "Advanced Settings" button. Check that "Active Virus Control" is enabled.
- Access the "Exclusions" tab.
- Click on "+" and add Dragon Nest SEA client files (dnlauncher.exe and dragonnest.exe).
- Ensure both client files are set as "Allowed".
- Click "OK" to finish.