cascade classifier training troubles

Hello, every time I try to enter> C:\opencv\build\x86\vc12\bin\opencv_traincascade.exe> -data C:\opencv\build\x86\vc12\bin\LETTER_TRAIN> -vec C:\opencv\build\x86\vc12\bin\LETTER.vec> -bg C:\opencv\build\x86\vc12\bin\LETTER_NEG.txt> -numPos 4 -numNeg 10 -numStages 15 -minHitRate 0.995 -w 50 -h 50 -featureType LBP -precalcValBufSize 1024 -precalcldxBufSize 1024 I get: > Train dataset for temp stage can not> be filled. Branch training terminated.> Cascade classifier can't be trained.> Check the used training parameters. What am I doing wrong? Thank you.