assertion failed

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on running this code an assertion failed error occurred on cmd line window

OPENCV Error : Assertion Failed <scn =="3" ||="" scn="4"> in cv::cvtColor,file:C:(address)

#include <stdio.h>
#include <iostream>

#include "opencv2/core/core.hpp"
#include "opencv2/features2d/features2d.hpp"
#include "opencv2/highgui/highgui.hpp"
#include "opencv2/nonfree/nonfree.hpp"
#include "opencv2/calib3d/calib3d.hpp"
#include "opencv2/imgproc/imgproc.hpp"

using namespace cv;

/** @function main */
int main()
{


    // Load the images
    Mat image1 = imread("scene11.jpeg");
    Mat image2 = imread("scene21.jpeg");
    Mat gray_image1;
    Mat gray_image2;
    // Convert to Grayscale
    cvtColor(image1, gray_image1, CV_RGB2GRAY);
    cvtColor(image2, gray_image2, CV_RGB2GRAY);

    imshow("image1", image2);
    imshow("image2", image1);

    if (!gray_image1.data || !gray_image2.data)
    {
        std::cout << " --(!) Error reading images " << std::endl; return -1;
    }

    //-- Step 1: Detect the keypoints using SURF Detector
    int minHessian = 400;

    SurfFeatureDetector detector(minHessian);

    std::vector< KeyPoint > keypoints_object, keypoints_scene;

    detector.detect(gray_image1, keypoints_object);
    detector.detect(gray_image2, keypoints_scene);

    //-- Step 2: Calculate descriptors (feature vectors)
    SurfDescriptorExtractor extractor;

    Mat descriptors_object, descriptors_scene;

    extractor.compute(gray_image1, keypoints_object, descriptors_object);
    extractor.compute(gray_image2, keypoints_scene, descriptors_scene);

    //-- Step 3: Matching descriptor vectors using FLANN matcher
    FlannBasedMatcher matcher;
    std::vector< DMatch > matches;
    matcher.match(descriptors_object, descriptors_scene, matches);

    double max_dist = 0; double min_dist = 100;

    //-- Quick calculation of max and min distances between keypoints
    for (int i = 0; i < descriptors_object.rows; i++)
    {
        double dist = matches[i].distance;
        if (dist < min_dist) min_dist = dist;
        if (dist > max_dist) max_dist = dist;
    }

    printf("-- Max dist : %f \n", max_dist);
    printf("-- Min dist : %f \n", min_dist);

    //-- Use only "good" matches (i.e. whose distance is less than 3*min_dist )
    std::vector< DMatch > good_matches;

    for (int i = 0; i < descriptors_object.rows; i++)
    {
        if (matches[i].distance < 3 * min_dist)
        {
            good_matches.push_back(matches[i]);
        }
    }
    std::vector< Point2f > obj;
    std::vector< Point2f > scene;

    for (size_t i = 0; i < good_matches.size(); i++)
    {
        //-- Get the keypoints from the good matches
        obj.push_back(keypoints_object[good_matches[i].queryIdx].pt);
        scene.push_back(keypoints_scene[good_matches[i].trainIdx].pt);
    }

    // Find the Homography Matrix
    Mat H = findHomography(obj, scene, CV_RANSAC);
    // Use the Homography Matrix to warp the images
    cv::Mat result;
    warpPerspective(image1, result, H, cv::Size(image1.cols + image2.cols, image1.rows));
    cv::Mat half(result, cv::Rect(0, 0, image2.cols, image2.rows));
    image2.copyTo(half);
    imshow("Result", result);

    waitKey(0);
    return 0;
}