Instead of manually checking SWC in setting, select your desired MovieClip in the library, and use the menu "Commands -> Convert Symbol to Flex Component" (or Container).
The first time you do this, Flash will set the proper settings.
Instead of manually checking SWC in setting, select your desired MovieClip in the library, and use the menu "Commands -> Convert Symbol to Flex Component" (or Container).
The first time you do this, Flash will set the proper settings.