An unhandled exception of type 'Emgu.CV.Util.CvException' occurred in Emgu.CV.dll Additional information: OpenCV: type == src2.type() && src1.cols == src2.cols && (type == CV_32F || type == CV_8U) in BOWImgDescriptorExtractor

Make sure the feature extractor used to generate vocabulary and the extractor given for BOWImgDescriptorExtractor are of same type. (E.g., SIFT)

More info:
http://stackoverflow.com/questions/15181699/error-in-bowimgdescriptorextractor-in-emgucv
http://code.opencv.org/issues/1879