In group registration i can see weird bits of code from the front-end
lass="eb-message">
and
ethod="post" name="adminForm" id="adminForm" action="/index.php?task=register.process_group_registration" autocomplete="off" class="form" enctype="multipart/form-data">
Look like it causes by something you entered into the message itself. Could you please submit a support ticket sending us super user account of your site for a quick check ?