It is possible that the plug-in has not been scanned correctly.
To force a re-scan of the plug-in, do the following:
Launch Cubase and choose "Plug-in information" from the "Devices" menu.
Click the "VST Plugins" tab and click the "VST 2.x Plug-in paths" button.
For Windows, please add
\Program Files\Steinberg\Vstplugins or your VST plug-in directory to the list of paths, then click "Ok".
For Mac, there is no need to add the path as the installer installs to the correct directory path.