problem in training the model using createFisherFaceRecognizer

i have been used opencv c++ library to detect faces and save theme to my desk then i make database with the images path and there labels. after call theme back to two vectors of the images and labels and use model1->train(images, labels); then model1->predict(face_resized, predictedLabel, confidence); the "predictedLabel" come with -1 value thought the training model have the images and labels please any help about what is the problem note:i use "haarcascade_frontalface_default.xml" in CascadeClassifier thanks Mohamed Sayed