Face problem in ‘prev & next’ button

I am using ‘Purnima’ template in my blogger. but I face some problem when I clicked on prev or next button. It does not work correctly.suppose I set 6 posts in one page. then on the first page it shows 6 posts, but it next page it shows 6 posts with few of the previous posts.and when all pages are complete, then it shows that some posts are missing.please check it with Purnima template and help me. I am really in a big problem with that.Thank you to all.