Error: Template not saved

Hello and congratulations for your work!

I am trying to use the ajax button in an archive page that displays company logos. (a custom post type I have created). No text, no title, no date. So my template is the following, but it wont be saved. Could you guide me on this?

Thanks in advance!

<li>
	<?php the_post_thumbnail(array(150,150)); ?>
</li>