I think you can sort the "End Time" column in the task list view, the earliest one should be the one that failed I suppose.
Of course, you can do the filtering through our powershell interface as below:
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$tasks = get-hpctask -jobId 13
foreach($t in $tasks){ if ($t.ErrorMessage.StartsWith("Task failed")) {$t.ID}}
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Obove command will show you the failed task number in job 13
Qiufang Shi