OK, the app bundle should not have folders in it called Voices or VoiceData. If the app bundle has these folders in it, the radio button selection in the “Add” dialog box at the time of importing the voice files is definitely on the wrong setting and the app will not be able to use NeatSpeech voices — you will get the exact error that you received.
The only thing you should see in the app bundle as a result of adding NeatSpeech are the loose files that can be found within the folder VoiceData (but not the folder itself) at the root level of the app bundle. The folder that says Voices has no purpose inside the app bundle since it just contains frameworks which get compiled directly into the app product binary. You should see groups called Voices and VoiceData in your project file navigator, but never in your app bundle.
Just remove the added folders from your project and add them again with the correct settings in the dialog box, exactly as they are described in the tutorial. This is the important line from the tutorial:
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.
“Create folder references” is selected in your add dialog currently — Xcode only has a single way of creating subfolders within an app bundle, and that radio button selection is it, so it’s the cause of the issue.
SLT will work fine because it doesn’t rely on any data files that need to be found in the app bundle.
If you want, you’re welcome to email me your project (with the classes and resources stripped out) and I can double-check what the issue is. If you want to do that, just send me a note via the contact form and I’ll send you the email address.