Is this occurring when you click the actual "INSTALL" button in the Steam client? As in, the Steam download is failing and the application isn't installed yet?
If so, that process is performed entirely by the Steam client and their CDN. VoiceAttack itself has no influence over it.
I did check, and the download and installation are working on my machine.
If you've tried rebooting, and the issue persists, you'll want to contact Steam about this.