unable to train using opencv_traincascade (window7 cmd)

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Hi

I dont seem to be able to train using opencv_traincascade whenever I created a vec file with a list of images that have the width as 80 and the height as 40.

And it keep showing me this error whenever I entered the following into the cmd.

opencv_traincascaded -data training -vec bananaSamples.vec -bg negative.txt -numStages 5 -minHitRate 0.999 -ma xFalseAlarmRate 0.5 -numPos 150 -numNeg 400 -w 80 -h 40 -mode -ALL

Error Message:

Training parameters are loaded from the parameter file in data folder! Please empty the data folder if you want to use your own set of parameters.

followed by this dialog.

but, I am able to train when I created a vec file with a list of images that have the size of 24x24. May I know why?