On the reference manual page, click on the 'advanced' button and you will see a 'marker' radio choice. It should show that 'Reference Manual' is selected. Change it to 'No Marker' and you should be able to generate the error after that.
On the reference manual page, click on the 'advanced' button and you will see a 'marker' radio choice. It should show that 'Reference Manual' is selected. Change it to 'No Marker' and you should be able to generate the error after that.