What does this mean (boxed in a red box) Please help!! I have so many intros but cant use many because of this problem. Any help?
The error means that Blender can't read or write to a specific codec. Speculation based on the screen shot:
your on windows, and probably don't have Ogg/Vorbis codecs installed on your system. You can download the OpenCodecs package, which will allow you to play ogg/ogv (vorbis/theora) on windows.
It's generally included in Linux/osx, so your probably getting examples from someone who works in one of those systems.
Or you could try setting the output of your render to a codec you probably already have like Mpeg, h.264, or Windows Media?