lkdemo.cpp crashing upon cornerSubPix() and calcOpticalFlowPyrLK() call

Hello there, I'm new to this forum, new to opencv and not that experienced as a C++ programmer, so please bear with me for a few seconds.. I recently tried to run the lkdemo.cpp (code below with comments for your convenience)

#include "opencv2/video/tracking.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include "opencv2/highgui/highgui.hpp"

#include 
#include 

using namespace cv;
using namespace std;

static void help()
{
    // print a welcome message, and the OpenCV version
    cout << "\nThis is a demo of Lukas-Kanade optical flow lkdemo(),\n"
            "Using OpenCV version " << CV_VERSION << endl;
    cout << "\nIt uses camera by default, but you can provide a path to video as an argument.\n";
    cout << "\nHot keys: \n"
            "\tESC - quit the program\n"
            "\tr - auto-initialize tracking\n"
            "\tc - delete all the points\n"
            "\tn - switch the \"night\" mode on/off\n"
            "To add/remove a feature point click it\n" << endl;
}

Point2f point;
bool addRemovePt = false;

static void onMouse( int event, int x, int y, int /*flags*/, void* /*param*/ )
{
    if( event == CV_EVENT_LBUTTONDOWN )
    {
        point = Point2f((float)x, (float)y);
        addRemovePt = true;
    }
}

int main( int argc, char** argv )
{
    help();

    VideoCapture cap;
    TermCriteria termcrit(CV_TERMCRIT_ITER|CV_TERMCRIT_EPS, 20, 0.03);
    Size subPixWinSize(10,10), winSize(31,31); // <------------------------------ subPixWinSize

    const int MAX_COUNT = 500;
    bool needToInit = false;
    bool nightMode = false;

    if( argc == 1 || (argc == 2 && strlen(argv[1]) == 1 && isdigit(argv[1][0])))
        cap.open(argc == 2 ? argv[1][0] - '0' : 0);
    else if( argc == 2 )
        cap.open(argv[1]);

    if( !cap.isOpened() )
    {
        cout << "Could not initialize capturing...\n";
        return 0;
    }

    namedWindow( "LK Demo", 1 );
    setMouseCallback( "LK Demo", onMouse, 0 );

    Mat gray, prevGray, image;
    vector points[2];

    for(;;) // <------------------------- THE FOR LOOP
    {
        Mat frame;
        cap >> frame;
        if( frame.empty() )
            break;

        frame.copyTo(image);
        cvtColor(image, gray, COLOR_BGR2GRAY);

        if( nightMode )
            image = Scalar::all(0);

        if( needToInit )
        {
            // automatic initialization
            goodFeaturesToTrack(gray, points[1], MAX_COUNT, 0.01, 10, Mat(), 3, 0, 0.04);
            cornerSubPix(gray, points[1], subPixWinSize, Size(-1,-1), termcrit);
            addRemovePt = false;
        }
        else if( !points[0].empty() )
        {
            vector status;
            vector err;
            if(prevGray.empty())
                gray.copyTo(prevGray);
// ==================================== CRASH B ================================================
            calcOpticalFlowPyrLK(prevGray, gray, points[0], points[1], status, err, winSize,
                                 3, termcrit, 0, 0.001);
            size_t i, k;
            for( i = k = 0; i < points[1].size(); i++ )
            {
                if( addRemovePt )
                {
                    if( norm(point - points[1][i]) <= 5 )
                    {
                        addRemovePt = false;
                        continue;
                    }
                }

                if( !status[i] )
                    continue;

                points[1][k++] = points[1][i];
                circle( image, points[1][i], 3, Scalar(0,255,0), -1, 8);
            }
            points[1].resize(k);
        }

        if( addRemovePt && points[1].size() < (size_t)MAX_COUNT )
        {
            vector tmp;
            tmp.push_back(point);
// ===================================== CRASH A =================================================
            cornerSubPix( gray, tmp, winSize, cvSize(-1,-1), termcrit);
            points[1].push_back(tmp[0]);
            addRemovePt = false;
        }

        needToInit = false;
        imshow("LK Demo", image); // <--------------------------- imshow()

        char c = (char)waitKey(10);
        if( c == 27 )
            break;
        switch( c )
        {
        case 'r':
            needToInit = true;
            break;
        case 'c':
            points[0].clear();
            points[1].clear();
            break;
        case 'n':
            nightMode = !nightMode;
            break;
        }

        std::swap(points[1], points[0]);
        cv::swap(prevGray, gray);
    }

    return 0;
}

I am using Visual Studio 2013, and the program compiles fine. When I tried to run the code, the first thing that went wrong was that "imshow()" would create a new window for each iteration of the loop. So, instead of rewriting over the previous image, imshow would create a new window entirely. I was able to solve this problem by creating a "string" containing the window name "LK DEMO" and replacing the name with the string variable in all functions. Now onto the big problem. Once I had the video up and running I tried clicking within the window to add a point for the program to track... CRASH! After commenting things in and out, and using several "cout" statements to pinpoint the troublemaker within the code, I finally found the place/s were the program would crash (which as the name suggests) are the calls to the function cornerSubPix() and calcOpticalFlowPyrLK(). I labeled the places where these are called in the code above as CRASH A and CRASH B. Once I reach CRASH A, I get the following warning in the screen:  And following this I press "Break" and the screen shows the following code (where I am assuming the code stopped)  Finally, after commenting "cornerSubPix()" I ran the program and a similar thing happened. This time, however, the program crashed when calling "calcOpticalFlowPyrLK()", CRASH B in the code above:  The following screen appeared after pressing "Break"  Now I am stuck and I don't even know how to proceed to solve this issue.. any suggestions would be greatly appreciated! Thank you in advance! Best, MrRed