TYPO3 Core

As of TYPO3 CMS 7.4, returning FALSE from a scheduler task's execute() method results in a "Serialization of 'Closure' is not allowed" error, locking the task for future executions. I tracked this down to the serialization of the exception that is thrown by the scheduler when logging it to the database (\TYPO3\CMS\Scheduler\Task\AbstractTask::unmarkExecution() line 427). It seems to be the topmost closure that's used in typo3/index.php to start the whole application which is disrupting the serialization.

This means, there's currently no way of gracefully ending an unsuccessful task execution. You either have to return TRUE to not block the task for future executions, or you'll have to unlock it manually after each run.