I just ran into this also. I can not add any new folder listings without this above problem using V 2.9.
I went to another site where I am running same Joomla 3.6.5 and an older version of EFL V 2.8 Feb 2012, and it works fine. I am able to add new folder listings and navigate to them without errors.
Can I download the older version somewhere until this is resolved?