[plt-scheme] find-method/who

I'm running into this cryptic error (using exp-tagged MrEd) and I
can't figure out what's going on:

compile: access from an uncertified context to unexported variable from module: |,/usr/local/plt/collects/mzlib/private/class-internal| in: find-method/who

I'm still trying to narrow down my code to track down what exactly is
triggering this, but I'm feeling less patient than usual so I figured
I'd post here in case anyone else has run into this before and can
save me some headache.

--dougo at place.org