After installing the Volta Audio Unit instrument plug-in, Logic must test it when it is loaded for the first time. If Volta fails Logic's Audio Unit validation tests, it is probably because you do not have the most recent iLok driver installed. You should download the current iLok driver installer for Mac OS X from PACE Anti-Piracy's website, www.paceap.com.

After the download has completed, run the installer, and then restart the computer. When you open Logic again, you will need to force the Volta plug-in to be rescanned. Open the Audio Units Manager by choosing Logic Pro menu > Preferences > Audio Units Manager. Select Volta in the list, and then click Reset & Rescan Selection.