Hello,
Maybe Tidy for PHP (http://php.net/manual/en/book.tidy.php) is not installed or enabled?
A 500 error is a generic PHP error and it should always being added to the log, we recommend to check your server configuration to find where are those errors added.
We also recommend you test the included samples (addText and embedHTML) using PHP CLI mode to check if the problem is from some missing PHP extension (ZIP, XML, Tidy), missing rw access, a license error or any other source.
Regards.