flashsocket.io Variable mx.utils::URLUtil is not defined

If you use Flash CS5.5 or other Flash CS for flashsocket.io.
Following error may occur.

Variable mx.utils::URLUtil is not defined 

Beucase flashsocket.io use Flex libarary(mx package).
I described how to use mx package with Flash CS5.5

1. Download Flex SDK 4.6 or any version from here.
2. Unzip it to any place.
3. Add "****FlexSDK\flex_sdk_4.6.0.23201B\frameworks\libs" to library path of Flash CS5.5.