You may need to reload your sounds. Just go into File>Preferences>Audio and press the "choose..." button. Navigate to your Notion 6/Sounds folder and press "Select" or "Select Folder." This will reload the sounds. If the problem persists, delete your electric bass sound file from your Sounds folder and download the Bundled Sounds Installer from your my.presonus.com account. Run the installer for the guitars and it should give you the electric bass back. If you get stuck, feel free to submit a support ticket using the "Support" tab in your my.presonus.com account.