I need to create a backup.

It currently says:

Warning: implode(): Invalid arguments passed in /home/***/public_html/inc/maintenance/views/_backup.form.php on line 80

This is line 80: $affected_paths .= implode( ', ', get_filenames( $basepath, $filename_params ) );

If I try to create the backup, this is what I get:

System backup is in progress...

Switching to maintenance mode...

Unable to switch maintenance mode. Maintenance file can't be created: «maintenance.html»

Switching out of maintenance mode...