1. Make sure you've downloaded the correct installer from the Korneff Audio site, for Windows it's the .exe file, for Mac it's the .pkg file, as well as updated to the most recent version of iLOK License Manager.
You can get your iLOK License Manager here.
2. Check if the plug-in is installed to the correct folder for your system.
For Mac, VST3 plug-ins should be in the following folder:
» Macintosh HD:/Library/Audio/Plug-Ins/VST3
AU plug-ins should be in the following folder:
» Macintosh HD:/Library/Audio/Plug-Ins/Components
For Windows, VST3 plug-ins should be in the following folder:
» C:\Program Files\Common Files\VST3
3. Confirm that your plug-in preferences and folders are correct in Ableton by opening Preferences>Plug-ins and checking the plug-in folder locations. If using VST3, turn on the Use VST3 Plug-In System Folders or User VST3 Plug-In Custom Folder.
If using AU, enable the system folder (Mac only).
4. Rescan your plug-ins by going to Preferences and clicking the Rescan button.