This can happen if you didn’t add the -ObjC other linker flag or if the voices weren’t added to your target when you imported the voices folder, usually due to something going wrong with this step:
“In order to use NeatSpeech, as well as importing the framework into your OpenEars-enabled project, it is also necessary to import the voices and voice data files by dragging the “Voice” folder in the disk image into your app project. Make sure that in Xcode’s “Add” dialog, “Create groups for any added folders” is selected. Make sure that “Create folder references for any added folders” is not selected or your app will not work.”
Also make sure that your app target is checked in that “Add file” dialog so the items which are being added are also being added to your target.
The error just means that the code for the NeatSpeechVoice “Emma” is not available to your project.