I went to the jwplayer site.
It appears in your code you are using the free player.
which they recommend a full url in the head tag.
meaning how you would reach the player using a browser.
http://www.mysite.com/ubbthreads/jwplayer/jwplayer.js
then on to the embed code they use relative paths.
so you may need to play with this some.
meaning
/ubbthreads/videos/Session1.flv
may become
/home/mysite/public_html/ubbthreads/videos/Session1.flv
or
../ubbthreads/videos/Session1.flv
or
../videos/Session1.flv

Not sure how they parse the paths.

Blue Man Group
There is no such thing as stupid questions. Just stupid answers