This error is due to a blank vacancy.
To see which vacancies are blank, you can create a query on Vacancies, tick the Job Description box, then apply Is blank filter. The active vacancies showing in the query with blank descriptions are the cause of the error.
When adding a vacancy, ensure of the following:
Job title has been entered into the job information field.
Experience, City, Country, and Experience fields have been populated.
The vacancy has been set to External or Both.
The closing date is in the future.
It is set as Active.
Job Description has been populated.