Why I can not get the sound even I chose "Interactive" mode?

To record sound from current swf file, please make sure "Stereo Mix" is set enabled and working. You can double-click "Volume" icon ("Sound" icon in Windows Vista) on Windows Taskbar to open the Volume/Recording Control panel (Sound panel in Windows Vista). You can also just click "Open Sound Panel" on the prompt to open the panel. And then enable "Stereo Mix" and choose "Set default" from command menu.
Please note that, in certain cases the configurations of recording device are different from Stereo Mix, as some sound cards offer different settings. Then you have to specify the right settings by yourself manually everytime before recording.