This was the first thing I checked. All of the files are on the server, in their proper folders. I had to first create a admin/boxes/extraboxes structure, as there was no "boxes" folder off of admin/

I just rechecked the server, and all of the files are present.

The downloaded ZIP archive of the Backup MYSQL plug in consists of:

admin readme.txt
includes/ backup_mysql.php
boxes languages
extra_boxes english
backup_mysqltools_dhtml.php backup_mysql.php


extra_datafiles
backup_mysql.php