If you are experiencing a behavior where a supposed inactive employee is being listed in the current modification history, you will need to first verify that the user account has been set to inactive.
To do this you can navigate to File > Set-up-> Employee > General.
Then you will also need to verify the employee's user access to see if they are set to inactive there.
Doing these two steps will mark that employee as inactive. They should not be able to access anything once completed.
If this employee is still showing in your recent modifications, you will need to have an ARMS support agent get connected to your database server to look at the specific CAD events the old employee is showing up under in the modification history.
Once ARMS support edits the database accordingly, your behavior will be resolved.