I've tried this twice on two different Unity projects so far. The first worked perfectly. The second one does not work. My 3D objects are always visible, as opposed to showing only when the target is being tracked. It appears the target is never found, since the 3D objects never change their orientations relative to the target.
I've followed the Compiling a Simple Project instructions several times now, and all settings and all files are identical in project that works and the one that doesn't work. I'm using one of the sample targets. What can cause this behavior?