I don't know why Tumblr code is generated every entry post. My code seems fine.
My page: http://paintloop.com.ar
My tumblr theme code: http://pastebin.com/iMd4vG5H
Without testing, it seems the theme is missing a closing {/block:Posts}
theme operator:
{block:IfEndlessScroll}
<div class="autopagerize_page_element">
{/block:IfEndlessScroll}
{block:Posts}
{block:Photo}
<div id="entry">
{LinkOpenTag}<img src="{PhotoURL-HighRes}" alt="{PhotoAlt}" width="{text:Width}"/>{LinkCloseTag}
{/block:Photo}
{/block:Posts}
{block:IfEndlessScroll}
</div>
{/block:IfEndlessScroll}
{block:ifnotendlessscroll}
<div id="bottom">
{block:Pagination}
{block:NextPage}<div style="float:right; "><a href="{NextPage}">progress</a></div>{/block:NextPage}
{block:PreviousPage}<div style="float:left"><a href="{PreviousPage}">regress</a></div>{/block:PreviousPage}
{/block:Pagination}
</div>
{/block:ifnotendlessscroll}