The scheduler should list the date a task was run for the last time. Is this date for your task several days old? If it is, the problem is with scheduler itself, at this point I'd try to review the properties of the task and perhaps also Windows Event log to see whether anything is amiss.
If the scheduler seems to be running your task, the problem might lie in the BAT file itself. Try to run the BAT file from the console. If it doesn't work, you'll obviously have to fix your BAT file. If it does work, try to run the scheduled task manually from the Task Scheduler (Run command on the context menu). If the BAT File doesn't work when run from the scheduler, my bet would be that it runs in a different security context and it's causing problems. You might want to change the user account under which the Scheduler runs the task in the Properties options - for example, set it to your own user account.
What's more fun is when you have automated systems connecting to the application. When its password changes the first thing that happens is that they can't connect, and within seconds after that they have retried 10 times and the application's user ID has been frozen by the security system.
subject: Windows scheduler not actively backing up MySQL dump