Recently I was having a problem where a Flash video was not being displayed.  It turned out the Flash video had not been created properly and had a dependency on other Flash files that were not available.  When I was viewing this Flash video directly using JBoss I did not see any errors.  But when I viewed it using Apache the logs showed the dependency problems.

Another developer, Allan Scott, suggested next time I use Charles or Fiddler as HTTP proxies.

Did you try watching the HTTP traffic with a tool like Fiddler or Charles?

If there is a dependency on something and it failed to download it then you should be able to see the 404 or some other error.