The email body is automatically set by the code. I don’t think that is the problem. However, I don’t know which field is empty. I’ve made a modified version of the Email.php file that will put info in the tmp/log/php.log (aka error log) file indicating which email field is empty.
Extract the Email.php file from the zip file and save it in your Inc/Claz folder over the version that is there. If you run cron, you can see what it puts in the error log and let me know.