I had the same problem/error, and solved it by putting
jrun.jar in c:\jboss-4.0.4.GA\server\default\lib.
I copied flex.war, flex-admin.war and samples.war to
c:\jboss-4.0.4.GA\server\default\deploy.
Also, you need to install the Flash Player 9.0 version that
comes with your install of FDS on each PC that will run a sample
app, otherwise you'll end up with just a background, and no samples
will start up.
All samples run, also in our network: PC W2K, PC WXP, MAC
OSX, etc.
As you can see I'm using the jboss-4.0.4.GA version of the
server (with EJB3.0; but i think it will work with other profiles
as well).
To obtain jrun.jar i first installed FDS with the jrun-server
option. In the directory structure you then will find jrun.jar.
Rui