It seems one of the strings you are adding is not being readed correctly. Please run one of the included examples (Core/embedHTML/sample_1.php) to test the conversion from HTML to DOCX using a tested script and then try to run each your script standalone (using PHP CLI for example) to know where the error comes from.
This simple script runs perfectly:
$docx = new CreateDocx();
$docx->embedHTML("<img src='http://www.somkiat.cc/wp-content/uploads/2016/07/ErrorMessage.jpg' />");
Maybe $body var has something wrong in it or if you are integrating it with a CMS or framework there's some error in how to have integrated the library. Please try to run your script standalone (out of any CMS or framework).
The trial package is the same than the Basic package but with the document properties overwritten, and image and text watermarks.