The correct answer is: incidental.
An incidental error is an error that is not intentional and does not affect the meaning of the text. It is a type of mistake that can happen to anyone, even the most experienced writers.
Intentional errors are errors that are made on purpose. They are often used for humorous or dramatic effect.
Conventional errors are errors that are made because the writer is not familiar with the conventions of a particular style of writing.
Usual errors are errors that are made frequently by many people. They are often the result of carelessness or lack of attention to detail.
Permissible errors are errors that are allowed in certain contexts. For example, errors in informal writing may be permissible, while errors in formal writing are not.
In the case of the newspaper article, the error is likely incidental. It is a small mistake that does not affect the meaning of the text. It is possible that the writer made the error accidentally, or that it was a result of a misunderstanding.