Normally this due to a corrupt task causing the snap-in to crash when navigating around.
If you was to browse to %windir% (windows directory normally c:\windows) then system32 and tasks, you can see all tasks created on a specific machine.
If you backup this folder and remove its content then try to load the task scheduler again hopefully this will resolve your issue. You can then copy the tasks back in one by one to try and locate the troublesome task.
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