When you use the array, you are assigning values to the individual elements.
prdImages.ImagesLoadStatus[i] = 0;
However, you do not assign the actual array. Add the one line:
ProductImages prdImages = new ProductImages();
prdImages.ImagesLoadStatus = new int[myArraySize];
for (int i = 0; i < prdImages.ImagesLoadStatus.Length; i++)
prdImages.ImagesLoadStatus[i] = 0;
And it should be fine.
[edit]Changed loop guard to array size - OriginalGriff[/edit]