TypeError: Error #1007: Instantiation attempted on a non-constructor

Scenario

Loading a SWF made from Flex 3 to a new Flash Builder 4 (new name for Flex) application.

Issue

An error pops out as follows:

TypeError: Error #1007: Instantiation attempted on a non-constructor.
at mx.preloaders::Preloader/initialize()[E:\dev\4.0.0\frameworks\projects\framework\src\mx\preloaders\Preloader.as:253]
at mx.managers::SystemManager/http://www.adobe.com/2006/flex/mx/internal::initialize()[E:\dev\4.0.0\frameworks\projects\framework\src\mx\managers\SystemManager.as:1925]
at mx.managers::SystemManager/initHandler()[E:\dev\4.0.0\frameworks\projects\framework\src\mx\managers\SystemManager.as:2419]

Reason

Flex application compiled on Flex 3 loads a resource rather a library. When this flex application loads the error comes in. To resolve this, you can either edit the mx namespace of that code to the new 2009 namespace or simply convert the said file/application to a FB4 version.

Generalization

It seems that other than the code and syntax itself, you cannot directly port or combine a Flex 3 application with a Flash Builder 4 app.