Can you please share the entire logging of the Workflow plugin by which the error occurs? Please make sure that it doesn’t contain any sensitive information.
A possible scenario in which the error may occur is when the database is locked by an user.
This looks to me like a security issue. The user is not authorized to log on to the database. So, either the username/password is wrong or the ip/host where the user is coming from is not authorized.
At this point it is probably better to submit a ticket via our support portal, because then someone from OL Support can assist you with the issue you’re facing.