Usually, you should not have any problems with flash videos. The 404 error indicates that somehow the path to the .FLV file got corrupted. Unfortunately, we do not have enough information to tell you what went wrong. Could you please explain in what scenario you use the flash video? Did you upload it from the Sitefinity File Manager? Is it on a separate directory on your server or on another server? Also how do you try to retrieve it? Do you have your own control on the page that references the path to the video, and how is that path constructed? Details like this would help us better understand where the error comes from. Thank you for the patience.
the Telerik team