After updating to the latest version of Animate CC (16.0.1), I'm no longer able to use Flash Builder 4.7. From Animate CC, I option-click on a library object and click "edit class", then choose Flash Builder as the editor. When I get into Flash Builder, I accept the default settings and create a new Flash Professional Project. Flash Builder doesn't import all the AS3 files necessary for editing. I also attempted starting a new Flash Professional Project from Flash Builder, selecting my project folder and .fla file, Flash Builder can't even finish creating a workspace.
Reverting back to the previous version of Animate CC (16.0.0) fixes the problem for now.