Invalid 404 Error – PHP coding error?

Hi, I am running a blog, https://www.manexperience.com, and when entering the front page, the last 5 posts are displyed in the main section, below the menu. Accoring to my theme, visitors, can click through the latest posts by clicking ‘next’ at the bottom. But when they reach the 3rd page, a 404 Error occurs, although this page should have posts.

So:
https://www.manexperience.com/page/1 works fine
https://www.manexperience.com/page/2 works fine
https://www.manexperience.com/page/3 returns an error

I have no idea where to look in the PHP coding, and where to look for an error. I am using the Arthemia theme, and apart from the menu it has not been much modified.

Thanks for any help, Aleks.