submitting more than 20 tasks at once causes ERROR QuartzSchedulerThread - ThreadPool.runInThread() return false! for some tasks

2017-03-28 22:51:37,569+0200 ERROR [nexus_QuartzSchedulerThread] *SYSTEM org.quartz.core.QuartzSchedulerThread - ThreadPool.runInThread() return false!

import org.sonatype.nexus.scheduling.TaskConfiguration
import org.sonatype.nexus.scheduling.TaskInfo
import org.sonatype.nexus.scheduling.TaskScheduler

import groovy.json.JsonOutput

class TaskXO
{
  String typeId

  Boolean enabled

  String name

  String alertEmail

  Map<String, String> properties
}

TaskScheduler scheduler = container.lookup(TaskScheduler.class.name)

for (i = 0; i < 100; i++) {
  TaskXO task = new TaskXO(typeId: 'script', enabled: true, name: "Script$i", alertEmail: null,
      properties: [language: 'groovy', source: 'println \'sleeping\'\n' +
          'sleep(10000)\n' +
          'println \'slept\'']
  )
  println "Creating $i"

  TaskConfiguration config = scheduler.createTaskConfigurationInstance(task.typeId)
  config.enabled = task.enabled
  config.name = task.name
  config.alertEmail = task.alertEmail
  task.properties?.each { key, value -> config.setString(key, value) }

  //create to run every second
  TaskInfo taskInfo = scheduler.scheduleTask(config, scheduler.scheduleFactory.cron(new Date(), '59 * * * * ?'))

  //create to run every an hour from now
//  TaskInfo taskInfo = scheduler.scheduleTask(config, scheduler.scheduleFactory.once(new Date(new Date().time + 3600000L)))

  JsonOutput.toJson(taskInfo)
}