Please see one of your other threads, there is a section on styling Meta Slider in the developer documentation on http://www.metaslider.com. As I said in another thread, strictly speaking we do not cover custom styling requests as part of free support.
It will probably be the default styling of Nivo Slider. I suspect it’s a CSS3 effect which is supported in FF and Chrome, but not IE. You’ll need to find that CSS and override it in your themes style.css file if you don’t want to see the shadow in Chrome and FF.