Multi-Page Categories Not Working

Hi, I just installed a new theme and all is working fine apart from the pages within categories. Please take a look at https://fewseconds.com
If you click on the arrow to the right you can access the second page of the main section, but if you go to Photos (on the top navigation) and click the arrow to go to the second page to see the rest of photos, I get an error (the page is designed to show 5 pictures only but there is a second page with more photos).

The people who design the theme have been trying to help me but they can’t replicate the error so they believe is something within my wordpress install. Could someone please help me?

Thanks a million,

Jo