Newer animations are in the HTML5-compliant MP4 format, using the H.264 codec. They should play well on all modern devices. Some of the older animations are in FLV format. Those are likely the ones you’re having trouble playing. To fix this, you need to have the latest version of Adobe’s Shockwave Flash Player plug-in installed. It’s available online for almost all operating systems and browsers. We are in the process of converting all our video content to MP4. Patience grasshopper.
The other possibility is that the video was embedded from an outside source, like Vimeo, and subsequently moved or deleted. That’s always a risk with external links. In that case, just do a search with the relevant key words and you’ll probably find it out there somewhere.