title: RUNNING BigQuery error in load operation: Invalid Credentials
body: <p>I am uploading files to my BigQuery account by using bq.py script.
  Once in a while I get the message "RUNNING BigQuery error in load operation: Invalid Credentials" with error code 1. However, checking the table, i see the data inserted properly.
  In job history all is ok.
  It is also happening while uploading from Google Cloud.</p>
  
  <p>I am running several scripts in parallel, using bash with cronjobs.</p>
  
  <p>What can be the problem and how can I avoid it?</p>