I just discovered a bug in step 1.2 (it's fixed on first page), which might cause creating images 0x0 pixels
In includes/image_utils.php find:
function resize_image($file, $quality, $dimension, $resize_type = 1, $height = 0) {
Replace it with:
function resize_image($file, $quality, $dimension, $resize_type = 1, $height = false) {