What is the type of video. Also, how big is it and when does it give you the
error (for example, right when you start, or after you go a while).
Sometimes hosts block certain file extensions from being uploaded or a site
can run over the size quota that an administrator can set.
Also, check your event log to see if something has been recorded under the
Application Event Log that would shed light on some internal error or more
detailed message from the server.