i am getting a bit creative (for me anyway) with my header for a new site,

i have a solid background pic(basic sunsety colours), and am sliding in the marquee a png pic above it(palmtrees and huts), it seems to work ok in preview till i allow blocked content, then the sliding png pic disappears.

have published it in my site and it seems to have the same problem there

anyone know what i am doing wrong, can you use png pics? or does the marquee just not support it?

thanks