[CS3] External API - onClick works but onLoad doesn't?

Hello! Please view the following link:

http://futureford.autofusion.com/Ext...dCallback.html

This is a simplified version of one of Adobe's examples of communicating to Flash from Javascript with the External API.

If you press the button under the flash movie, the function callExternalInterface() is fired and the ball in the Flash movie moves. Trying to fire the same function via onLoad in the <body> tag, however, gives this error in Firefox:

Code:

Error: getMovieName("myMovie").callPlayBall is not a function Source File: http://futureford.autofusion.com/ExternalInterface_addCallback.html Line: 16

In IE6, it works just fine.

Any ideas on why FF says it's a function if it's called via onClick, but it's not a function when called via onLoad? That makes no sense to me. :confused:

Any help is GREATLY appreciated.