I have this error too. GroupX not working.
You can do this:
1. You can directly edit the file:
plugins/cck_field/group_x/assets/js/script.js
106 - ind_group = id.slice(last_index+1).toInt();
+ ind_group = id.slice(last_index+1);
277 - num_group = num_group.toInt();
+ num_group = num_group;
but it is overwritten when updating. (not recommended). Maybe you have a better solution
2. Turn off old jquery.ui.min.js and download new in index.php of your template
$doc = JFactory::getDocument();
unset($doc->_scripts[$this->baseurl.'/media/cck/js/jquery.ui.min.js']); // remove old
$doc->addScript('http://code.jquery.com/ui/1.11.4/jquery-ui.min.js'); // download new
this will solve the problem with an error when deleting items.