One of the challenges all web developers face is future versions of platforms your application runs on. When a new browser or in this case version 10 of the Adobe Flash Player is on the horizon, it's good to run your application against it to see if any changes will need to be made before the new version goes to production and screens across the Web light up with messages of "An upgrade is available."
We've recently launched an unsupported version of our AS3 API for those of you working with Flash 10. Some developers have found that our 5.3 release and it's version checking of the Flash Player would cause errors to be thrown. This unsupported release (5.3.1_U) fixes that.
For the curious, it's an unsupported build because the Flash 10 player is still in development. This update will however allow you to run and test your applications on Flash 10 using the MapQuest AS3 API.