Why is Windows Task Scheduler trying to launch multiple instances?

Solution 1:

This is the issue described in KB2617046: if you disable and then enable a scheduled task, duplicate triggers are created. The task properties still shows only one trigger, but you can see that the task is triggered multiple times simultaneously in the task history.

There is a hotfix available from Microsoft. The hotfix says it is for Vista, but it works on Server 2008 SP2. After applying the hotfix, you have to disable and then re-enable the trigger on your task (closing the trigger properties window in between to apply the changes) in order to get rid of the duplicates.

Solution 2:

We managed to stop Windows Task Scheduler starting up multiple processes by ticking the option "If the task fails, restart every:" with the defaults of "1 minute" and "Attempt to restart up to: 3 times".

This seemed counter-intuitive as

1. the tasks did not appear to be failing (the actions they perform got run multiple times)

and 2. the tasks already seemed to be deciding to start three times anyway.

Also - we have these same tasks setup on Test webservers and have not needed to tick this option.