Hey, just thought I'd post this in case you wanted to edit the puzzle, but I believe that there might be two solutions as the highlighted bit *does* have two full crosses attached to it.  Otherwise, such an addictive puzzle game; very well done.

Hi, the highlighted pixel has 3 happy pixels in this image, itself and one to its left have full crosses, and also the pixel that's left top from the highlighted pixel is happy, as it is against the wall and surrounded by pixels. So I don't think there is a problem here.