Registering a plugin function with arguments

plugin = krpano.get(evt.data);
plugin.fname = fname;
function fname(arg:String):void {
....
}

Does not work. The error is: WARNING: Unknown action command: plugin[name].fname

How can I pass an argument to one of my plugin functions?

After more experiments, it looks like I'm completely unable to add a function to a plugin; I always get this error

Got it working somehow. I think it had to do with me calling it from onxmlcomplete; Apparently the register event for the plugin was being fired after this one (?) Anyway, I'm using it with preload="true" now, which I think is what fixed it.