Face Detection System using Gabor filter(Neural Network)

i have download the file at http://www.mathworks.com/matlabcentral/fileexchange/11073-face-detection-system, and i have run this program, the result shows up but do not accurate for certain image, some face cannot be detected for certain image and sometime it detect the other object in the image as a face, why it happens and how to solve this problem, i am newbie with MATLAB and kindly lost right now how to find a way,could someone please help me..??