Black screen, lost synching, audio cutouts for vpn users

I'm working on a Storyline project and many (not all) of the viewers will be using IE 8. In tests, we've already encountered problems of blacked out screens when the program starts to run (usually the scene comes into view partway through the first slide). We've also found that the program loses its synching for some remote viewers sometimes, and there are also audio glitches that show up for some people some of the time. These usually show up when people are using the virtual private network (which will be used by many of the target audience. Is there anything that can be done? And is this related to the version of IE that is being used, or are there other causes? These problems make the program virtually worthless for many who will be using it...

Thanks,

Carla