This happens when a job ends in error that has the Continue After Error flag set to 'N'.
For additional information on this flag see the following: https://www.blackbaud.com/files/support/guides/ta5/Spctv33/Setting_the_Continue_After_Error_Parameter.htm
Once the job is identified that ended in error, go to the Schedule Administration screen, highlight the job in question, and press the “Clear” button.After clearing the job, the queue log will show the following: "Error has been cleared on <date> at <time>. Resuming processing."
If the issue persists after taking the action indicated, or if you have questions, please create a support request at www.blackbaud.com/support providing the details of the issue and referencing this solution.