I'm running mysql on a server, and I've created a backup project. I've also set the schedule for the project to be 7:00 am every day, but it doesn't run on schedule (well, ever actually).
I can manually run the backup project (and often do, I restore the backup file to a test db schema for usability tests and the like) so I know the project is fine... it's just the scheduling part.
I should also note that the account that I use on the server is always logged in (long story, don't ask). Could that be the problem?
This thread on the mysql support forums seems to cover what you're running into. It suggests that the problem may be with the user/password used for the scheduled item, or possibly that it needs to be run by hand from the scheduled items control panel at least once for it to be registered properly. You may find your answer in that conversation.
Have you considered just running a mysqldump from a windows scheduled task?
I know this is an ancient thread, but I had a similar issue recently with Windows 2003 Server scheduled backups not successfully executing. The scheduler log showed starting of the backup task, but stopping 19 sec later without a reported error. Manual backups usually worked, but didn't sometimes. I found that 19 sec corresponded to how long it took to open a folder on the external drive I was writing to, if the external drive had not been accessed recently.
Finally got success with backups by leaving Windows Explorer open and pointing to this external drive.