Access Violation Writing Error... primitive integers

Question

I'm creating a heightmap in DirectX11 and I'm getting an Access Violation Writing location when I assign the terrain height to be that that is in the bitmapInfoHeader.

bool HMTerrain::LoadHeightMap(char* filename)
{

FILE* filePtr;
int error;
unsigned int count;
BITMAPFILEHEADER bitmapFileHeader;
BITMAPINFOHEADER bitmapInfoHeader;
int imageSize, i, j, k, index;
unsigned char* bitmapImage;
unsigned char height;

// Open the height map file in binary.
error = fopen_s(&filePtr, filename, "rb");

if (error != 0)
{
    return false;
}

// Read in the file header.
count = fread(&bitmapFileHeader, sizeof(BITMAPFILEHEADER), 1, filePtr);
if (count != 1)
{
    return false;
}

// Read in the bitmap info header.
count = fread(&bitmapInfoHeader, sizeof(BITMAPINFOHEADER), 1, filePtr);
if (count != 1)
{
    return false;
}
// Save the dimensions of the terrain.
_pTerrainWidth = bitmapInfoHeader.biWidth;     // THIS IS THE BREAK
_pTerrainHeight = bitmapInfoHeader.biHeight;

// Calculate the size of the bitmap image data.
imageSize = _pTerrainWidth * _pTerrainHeight * 3;

// Allocate memory for the bitmap image data.
bitmapImage = new unsigned char[imageSize];
if (!bitmapImage)
{
    return false;
}

// Move to the beginning of the bitmap data.
fseek(filePtr, bitmapFileHeader.bfOffBits, SEEK_SET);

// Read in the bitmap image data.
count = fread(bitmapImage, 1, imageSize, filePtr);
if (count != imageSize)
{
    return false;
}

// Close the file.
error = fclose(filePtr);
if (error != 0)
{
    return false;
}
// Create the structure to hold the height map data.
_pHeightMap = new HeightMapType[_pTerrainWidth * _pTerrainHeight];

if (!_pHeightMap)
{
    return false;
}

// Initialize the position in the image data buffer.
k = 0;

// Read the image data into the height map.
for (j = 0; j<_pTerrainHeight; j++)
{
    for (i = 0; i<_pTerrainWidth; i++)
    {
        height = bitmapImage[k];

        index = (_pTerrainHeight * j) + i;

        _pHeightMap[index].x = (float)i;
        _pHeightMap[index].y = (float)height;
        _pHeightMap[index].z = (float)j;

        k += 3;
    }
}
    // Release the bitmap image data.
    delete[] bitmapImage;
bitmapImage = 0;

return true;
}

///////////////////////// HEADER FILE /////////////////////////
class HMTerrain
{
private:
INT                         _pTerrainWidth, _pTerrainHeight;
int                         _pVertexCount, _pIndexCount;
ID3D11Buffer*       _pVertexBuffer, *_pIndexBuffer;

HeightMapType*  _pHeightMap;


bool                            LoadHeightMap(char*);
bool                            InitialiseBuffers(ID3D11Device*);

void                            NormalizeHeightMap();
void                            ShutdownHeightMap();
void                            ShutdownBuffers();
void                            RenderBuffers(ID3D11DeviceContext*);

public:
HMTerrain();
HMTerrain(const HMTerrain&);
~HMTerrain();

bool                            Initialise(ID3D11Device*, char*);

void                            Shutdown();
void                            Render(ID3D11DeviceContext*);

int                         GetIndexCount();
};

_pTerrainWidth is an int. While biWidth is a DirectX LONG. I believe that is the issue but when I change _pTerrainWidth to a DirectX LONG I still get the same violation error on the same line.

Any ideas would be much appreciated :-))