title: Jenkins not executing jobs (pending - waiting for next executor)
body: <p>Jenkins won't execute any jobs. Having viewed <a href="https://stackoverflow.com/questions/8499764/jenkins-job-is-waiting-for-next-available-executor">this question</a>, I have disabled all slave nodes but a simple job won't even run on the Master node.</p>
  
  <p>What is wrong?</p>