Custom libraries suddenly don't load

Running final 2.x version of CI for this particular app.  App has been running since mid-2013.

Custom libraries no longer load.  I checked logs and the default controller's constructor simply ends after loading helpers, etc prior to hitting the first custom library.  Three custom libraries are supposed to load in order.

CI simply display a white page.

This app has a backend to it and it loads fine.  Only controllers with my custom libraries (which have been running fine until this AM) fail to load.

Any clues on what I shoudl do to tryt o fix the issue?  I've spent all day on this with no luck.  (I shoudl say that I'm not new to CI, have 7 other CI websites all running on the same shared host (Media Temple).  SOme use the same version of CI and some use the latest version, depending on when they were initially put into service.

Thanks for any help you can provide!