After more testing I discovered easypopulate-4.0-master (configuration part) cannot be installed AFTER fec.
Something to do with the database fields not matching (Haven't narrowed it down)
My work around was to install ep-4 first and then css_js_loader & fec.
This seems to work on a fresh install (classic template).

I am loading 4 other modules so I'll report back if I have success (or failure) on my full blown site.