in the webassist/email/waue_CONTACT-FORM-NEW_1.php file, change line 140:
$MailBody = $MailBody . ((isset($_POST["Product_Group"]))?implode(",",$_POST["Product_Group"]):"");
to:
$MailBody = $MailBody . ((isset($_POST["Product_Group"]))?$_POST["Product_Group"]:"");
there is no need to use implode there, you already have code to implode the form element at line 1 of the contact form page.