I am using Adobe Flash Builder 4. I've run into this issue with my latest project, but I was able to re-create it with an almost empty project. Here is what I've done. Created a new Flex Project Created a locale/en_US folder within this project. Added a class that extends SparkDownloadProgressBar. All this class does is attempt to create a Label. When I try to debug this application, I get the following error. Error: Could not find compiled resource bundle 'components' for locale 'en_US'. at mx.resources::ResourceManagerImpl/installCompiledResourceBundle()[E:\dev\4.0.0\frameworks\projects\framework\src\mx\resources\ResourceManagerImpl.as:340] at mx.resources::ResourceManagerImpl/installCompiledResourceBundles()[E:\dev\4.0.0\frameworks\projects\framework\src\mx\resources\ResourceManagerImpl.as:269] at mx.resources::ResourceManagerImpl/processInfo()[E:\dev\4.0.0\frameworks\projects\framework\src\mx\resources\ResourceManagerImpl.as:387] at mx.resources::ResourceManagerImpl()[E:\dev\4.0.0\frameworks\projects\framework\src\mx\resources\ResourceManagerImpl.as:122] at mx.resources::ResourceManager$/getInstance()[E:\dev\4.0.0\frameworks\projects\framework\src\mx\resources\ResourceManager.as:111] at mx.core::UIComponent()[E:\dev\4.0.0\frameworks\projects\framework\src\mx\core\UIComponent.as:3728] at spark.components.supportClasses::TextBase()[E:\dev\4.0.0\frameworks\projects\spark\src\spark\components\supportClasses\TextBase.as:154] at spark.components::Label()[E:\dev\4.0.0\frameworks\projects\spark\src\spark\components\Label.as:384] at Preloader()[C:\SVN\Games\Social\Test\src\Preloader.as:21] 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] The Flex Compiler/Additional Compiler Arguments section does contain "-locale en_US", but I do not want to just remove this as I am planning to have this load different property files based on the localization region at run-time and how I understand it, I will need to add each locale that I am planning to use on the compile argument line. I am at a loss as to how to attack this problem. If you need anymore information from me to help with this, I will be more than happy to provide it. Thanks ahead of time for the help!