Today someone at work kept getting the Fusebox 4 “Circuit Not Defined” error at random with an application he was working on, and instantly I remembered something about Fusebox 4 which would probably cause this problem. Even when his app was in developer mode, it kept having the circuit problems.

What I remembered was that the default application name in Fusebox 4 core files is “wireframeFB4″ (at least in version 4.03). If you are running multiple applications in Fusebox 4 on a server, they will all be fighting for what the Fusebox configuration should be within the FB4 Application scope if you haven’t changed the default application name.

Long story short, create unique names within each <cfapplication> tag for each instance of a Fusebox 4 application which you have running on a server, and these problems will go away.

I believe I’ll send a bug / feature request to have them use a dynamic application name much like Mach-II so that by default it will not create conflicts like this.