An "Access Denied" error message means that the Windows user account running the backup job does not have access to read the file content.
Current versions of Magnus Box automatically creates a service account with all necessary permissions to read local files. If you are experiencing "Access Denied" errors, you may be trying to back up a network path that has been mounted as a directory. Please see the "Accessing Windows network shares and UNC paths" for more information.
If you are experiencing "Access Denied" errors and you are certain that you are not backing up a mounted network path, please contact support.