It is possible that the plug-in has not been scanned correctly.
To force a re-scan of the plug-in do the following:
The plug-in has been installed into C:\Program Files\Steinberg\Vstplugins
Wavelab 6 : Choose Options > Preferences. Click the VST tab.
Wavelab 7 or above : Choose Options > VST Plugin Settings.
Below where it says "Optional Extra VST Plugins folder" click the folder icon on the right and locate the VST folder.
Click "Force plug-in detection at next start"
Click OK and quit Wavelab.
Restart Wavelab and the plug-in will be rescanned. The plug-in should now show up in the list.
Wavelab 7 or above
The plug-in has been installed into HD/Library/Audio/Plug-Ins/<VST or Components folder>
In case 32-bit and 64-bit versions of WaveLab are used on the same system, their settings are shared. An exception to this rule are the following options in the Plug-in settings dialog:
This is because 32-bit plug-ins cannot beused in WaveLab 64-bit and reciprocally.