I've run into this issue twice now and am wondering the best practice for the field mapping. Initially when creating visualizations based on text I was using fieldname.raw. I then had the "Field data loading is forbidden" error pop up and found switching the field name to fieldname resolved the issue.
Today, I received the same "Field data loading is forbidden" error when loading visualizations and changing the fields back to fieldname.raw got everything going. Just wondering why the field seems to be flipping between fieldname and fieldname.raw.
This is on Kibana 4.6.1, Elasticsearch 2.4.0 and Logstash 2.4.0