page/2/ — what is this?

So I have never seen this before. I dont know what I did in my settings but now every time I click back (to see older posts in a category) i see /page/2 and that redirects me to a 404 page sayig -it doesnt exist….

Its not a theme issue…what would cause this? my current perma link is /%category%/%post%/ (spelling may not be the same)…

What I should state is that this isn’t on one site, its a network wide issue