There's an incompatibility issue with article2pdf and WP-Syntax.
If you include an HTML img tag in a WP-Syntax
pre block, article2pdf will try to include that image in its output -- but if the image doesn't actually exist on your server, that will cause errors.
For example, if you have this WP-Syntax code in a post:
<pre lang="xml"> <img src="1.jpg" alt="" /> </pre>
article2pdf will throw an error, because there is no 1.jpg located at the same directory level as the permalink / URL of the page.
I don't want to branch this code without the author's permission so I am not going to provide a workaround. If you disable the display of images in the settings for article2pdf, this problem will not happen (but, of course, correct images in your posts won't show up, either).