Something wrong

i have setted my content type to:
include
node title
Only nodes with same content type

blocks: 0

in page.tpl

       <div class="nav-previous"><a rel="next" href="<?php print  prev_next_nid($nid, 'prev');?>"><span class="arrow">prev</span></a></div>
      <div class="nav-next"><a rel="prev" href="<?php print  prev_next_nid($nid, 'next');?>"><span class="arrow">next</span></a></div>

everything seems fine, but the link is the same in both, prev and next links.