I use Windows Task Scheduler to run automated tasks. Occasionally I will see that randomly a task has failed to perform its duties. When I check Task Scheduler to see what has occurred in the history log, I see that for some reason, when the tasks are triggered at their schedules, they are spawning several instances of themselves simultaneously which turns into a train wreck for the task and it either kills the other instances and tries to run the "first" one, or it just does not run at all as it believes another instance of itself is already running. Sometimes this occurs in the same tasks and then occasionally it happens with others. The fix is just to end all instances and start the task manually.


Why would one single task with one single schedule decide to spawn multiple instance of itself simultaneously?


I've got a separate user account set to run the tasks instead of myself. That user is indeed an admin on the machine that runs the tasks and the tasks are set to tun whether or not the user is logged on. Also, the machine is windows server 08 R2.

  • Is this an exe file set to execute, or a batch file? How often is it set to execute, every 15 minutes, every hour, daily? You might also check the c:\windows\Tasks\SCHEDLGU.TXT to see if you find anything to note from that. – Nixphoe Jun 2 '11 at 19:14

There is a known bug with task scheduler that will cause it to run the same task twice from time to time. It happens when the previous scheduled task terminates exactly when the new task is supposed to start: the scheduler will then run the same task twice.

There is a hotfix available there: http://support.microsoft.com/kb/2461249

When we ran into that problem, we fixed it simply by making the task run less frequently.


The task scheduler has an option of restarting a task if it thinks the first start was not successful. If the option is set, it would be a good idea of disabling it. Some further examination as for why the first start returns a non-successful value should follow.

Could you post what exactly you are starting and if it is a script of some sort include the source code of the script as well?

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