There's a typo in the following part of the book:
ORA-27469: string is not a valid string attribute
Cause: A non-existant attribute was specified.
Action: Reissue the command using a valid attribute for that specific scheduler object.
To be specific, the typo is in the word 'non-existant'.
Thank you for pointing out this typo. The writer with overall responsibility for the error messages manual has been notified. However, the actual text (including Cause and Action) for the messages is extracted from the development source message files. The developer responsible for that specific message will be contacted to make the correction.