Welcome,
That is going to be due to something about the path to the acoustic model or the process of adding the bundle to the app. Make sure that the model is added successfully to the target you are running and that the path you are passing to the model is correct. The best way to do so is to instantiate an NSFileManager instance and use it to check whether the contents of your acoustic model are available at runtime and located where you expect them to be. Troubleshooting custom acoustic models and their components are outside the scope of support here, but this is a good starting point for troubleshooting the existence of files in various parts of your app:
http://stackoverflow.com/questions/1638834/how-to-check-if-a-file-exists-in-documents-folder
After verifying to your satisfaction that the file exists, if you still have trouble, take a closer look at whether you are using OEAcousticModel’s convenience path methods identically to how they are used for the shipped models.
Good luck!