Search Engine Friendly URLs 404 Error

I was practicing lesson 14 to set "Search Engine Friendly URLs" in the Global Configuration, and after I did so, the pages did not load correctly and I got "404 - Article #25 not found".

I tried going back to the former setting and that worked at first but then I tried to reset one more time and the pages won't load correctly with either setting. I am using the "Bolt" template.

Please advise me how to get the pages to load properly with the Search Engine Friendly URLs in effect.

Thank you.

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