Error 2036 from loadClip using AS2

Question

I'm troubleshooting an old AS2 application, particularly where it is loading a swf into an empty movie clip. We're a secure site, but the clip to be loaded is on the same domain.

We tested loading a clip from a non-secure http address, and the swf successfully loads:

//Throws Error #2036: Load Never Completed
my_mcl.loadClip([valid path], emptyMovieClip);

//Successfully loads clip:
my_mcl.loadClip("http://[valid IP address]/a.swf", emptyMovieClip);