Sound Studio uses "sandboxing" that disables audio plug-ins from doing things like activating over the internet. If you plan on using SoundSoap in Sound Studio, we recommend you do the activation of SoundSoap first with another host application like Garageband, Peak, Logic, etc. After you have activated SoundSoap, you should be able to use it in Sound Studio without any issues.
Also, please see this related article:
Free Alternative App for Activation
After launching AU Lab, press the "Create Document" button in the dialog that appears. A mixer graphical user interface will appear, with an area titled "Effects". Here you can select Antares>SoundSoap and enter your activation information.