Cause:
The error is caused by the AUTOINDEX-Workflow displayed in the error message and has a negative effect on other Workflow processes as well.
Solution:
Start the Administration and open the displayed AUTOINDEX-Workflow. To achieve that the settings are correctly entered into the database again changes have to be made. For this, you can simply write something in the "description" field (or change the content of this field).
After that you store your changes. Do this also for the other existing AUTOINDEX-Workflows.
(Note: If error messages occors while you doing your changes click on ignore and go on changing further AUTOINDEX-Workflows).
After you changed all of your AUTOINDEX-Workflows the error message should not occur anymore.