New Post: AccessViolationException when accessing pixel color (GetPixel())

Ive been trying to follow this suggestion but havent been able to so far. How should I change it to make this work?

The crazy thing here is that this work for a larger image (full hd) but not for a 512x424 image.

This is the code im using:

 private void SumPictures( WriteableBitmap currPicture )
        {     
            for (int col = 0; col < currPicture.PixelWidth; col++)
            {
                for (int row = 0; row < currPicture.PixelHeight; row++)
                {
                    Color currPixel = currPicture.GetPixel(col, row);  //<-- Error happens here. The console output prints the PixelWidth and PixelHeight correctly
                    Console.WriteLine("Col: " + col + " row: " + row + " currPicture.PixelWidth: " + currPicture.PixelWidth + " currPicture.PixelHeight: " + currPicture.PixelHeight);

                    _sumedAllImages[col][row].R += currPixel.R;
                    _sumedAllImages[col][row].G += currPixel.G;
                    _sumedAllImages[col][row].B += currPixel.B;
                    _sumedAllImages[col][row].A += currPixel.A; 
                }
            }
        }

        private void LoadAndAverageImages(string filePrefix)
        {
            string[] allPictures = Directory.GetFiles(selectFolder(), filePrefix + "*.png", SearchOption.AllDirectories);            

            //for (int i = 0; i < allPictures.Length; i++)
            Parallel.For(0, allPictures.Length, i =>
            {
                _filenameList.Add(allPictures[i]);
                WriteableBitmap currPicture = new WriteableBitmap((BitmapSource)(new BitmapImage(new Uri(allPictures[i]))));
                SumPictures(currPicture);
                if (i == 0)
                    _samplePicture = currPicture;
                Console.WriteLine("currPicture: " + i);
            });           

            for (int col = 0; col < _samplePicture.PixelWidth; col++)
            {
                for (int row = 0; row < height; row++)
                {
                    Color currPixelSum = new Color();
                    currPixelSum.R = (byte)_sumedAllImages[col][row].R;
                    currPixelSum.G = (byte)_sumedAllImages[col][row].G;
                    currPixelSum.B = (byte)_sumedAllImages[col][row].B;
                    currPixelSum.A = (byte)_sumedAllImages[col][row].A;

                    _samplePicture.SetPixel(col, row, currPixelSum);
                }
            }

            Console.WriteLine("Loaded " + allPictures.Length + " pictures!");
        }

Thank you!