This error means that there is a conflict between GameGuard and another running security solution most likley from running another non-NCSOFT game at the same time.
To resolve this issue, please close any other programs that are running before attempting to launch Lineage 2 again. If you continue to receive this error after closing out all other programs, you may need to restart your PC to ensure whatever application was causing the conflict is properly terminated.
If you continue to experience an issue, please contact Technical Support by logging in and submitting a ticket HERE.