Help validating xhtml…

I am having trouble getting a short line of code to validate. The page is at https://www.babybumps.net/blog/?p=29

The section involved is the code to create the previous and next entry links at the top of the content area. The code I am using is:

<div class="navigation">
<strong><div class="previous"><?php previous_post_link('&laquo; %link') ?></div>
<div class="next"><?php next_post_link('%link &raquo;') ?></div></strong>
</div>

If you click on the “Valid xhtml” link at the bottom you can see what errors I am getting but I can’t figure out how to recode this. Any suggestions?