When Customizing the LiveCycle Workspace ES2 User Interface [link] guide was released, it was before Adobe Flash Builder was available for us to do our certification testing. Technically, it is possible to use Flash Builder provided you use the Flex SDK version 3.4.1, ant-contrib.jar file version 1.0b2, and Ant-plug-in as described in the guide. For more information, see the LiveCycle Product blog for steps in the posting Customize LC Workspace ES2 UI using FB4 Premium on 64-bit O/S
In a future release, we plan to complete certification testing and update the guide with updated instructions, but in the meantime, here are some instructions for you to configure your environment to build Workspace customizations using Flash Builder 4. You must complete the last step in the blog when your development environment is a 64-bit operating system.