Allegro collision detection

bool Player::collide(int x, int y, BITMAP* object)
{
    for (int px = 0; px < 20; px++)
    {
        for (int py = 0; py < 20; px++)
        {
            if (getpixel(image,px+x,py=y)!=bitmap_mask_color(image))
            {
                if (getpixel(object,xPos+px+x,yPos+py+y)!=bitmap_mask_color(object))
                {
                    return true;
                    break;
                }
            }
        }
    }
    return false;
}

xPos and yPos speak for themselves
x and y are the potential changes to the xPos and yPos, if this method returns false, they will be made.
image is a 20x20px player image.
object is my arena made from a tileset, pieced together by a vector of strings, each character in the vector representing a tile.

However, my player resolutely refuses to fall when gravity tells him to, or the program crashes. Either he's colliding with something (He shouldn't be, he's surrounded by masked squares) or some crazy voodoo is eating my datas.

any ideas?

>>8
Looks better.

>>1
Now you have four problems.

DON'T HELP HIM