It’s likely that re-importing the acoustic model files individually fixes something minor that has gone wrong a bit earlier in the process with the addition of that folder (for instance if the target was accidentally unchecked while adding or it was added as a reference and the reference was somehow problematic or became so later) so I strongly endorse gregquinn’s method described above as a troubleshooting step if you see a crash when listening starts.

I have the definitive answer to why this is sometimes happening — OpenEars requires that everything added to mainBundle is added at the root level (just because I don’t want to open up the can of worms of either trying to figure out at what level some crucial file is added, or forcing the developer to declare it for every file that the framework uses) and in the “add file” dialog in Xcode, if the option “Create folder references for any added folders” is selected, Xcode will create a folder inside the app’s mainBundle and put the files in there. So the acoustic model files were almost certainly in your app, but they probably couldn’t be found by the framework due to being in their own directory. I have improved the documentation to make sure this is clear and I appreciate your drawing my attention to the fact that it was a pitfall.