That means the acoustic model is not added to the app bundle, or you are passing something other than the path to the acoustic model to a parameter which requires that path.
The first step for you in troubleshooting this is to verify whether the acoustic model was added to the bundle in the required way. There is an explanation in the tutorial about the settings required when adding the OpenEars Framework folder contents to your app: https://www.politepix.com/openears/tutorial
If the acoustic model is available in your app, you will be able to see it at the root level of the main bundle when you download the app container from your device.
If that isn’t the issue, check out the sample app or tutorial to see how the acoustic model path is referenced and passed to the various methods that use it (usually it would need to be referenced by the OEAcousticModel convenience method [OEAcousticModel pathToModel:@”AcousticModelEnglish”]). That is the next likely reason for this issue.
It’s known to work, so this will end up being due to some minor oversight like one of these two things.