Any of those help You will need to modify the entry in the solr.xml file that is in the root of where your Solr instance is running and add at least one entry. Below is the example that comes with the Solr distribution.
With these it helps I'm having the same issue, but I imagine its because they removed that class from 6.1 (or sometime after 5.3). Removing the element from solrconfig.xml in the problematic core worked for me and should hopefully do the trick for you as well.
<!-- find this line in your solrconfig.xml and comment/remove it -->