Hello Mark,
You can either validate the plug-in manually, if the Plug-in Manager in Logic's Preferences lets you do that.
Or you can reset your AU Cache, if that doesn't work:
In the Finder, choose "Go" > "Go to Folder" from the menu.
Type ~/Library/Caches in the "Go to the folder" field.
Press the Go button. Remove the "com.apple.audiounits.cache" file. Remove the ~/Library/Caches/AudioUnitCache folder.
Restart your computer, all plug-ins will be scanned again.
Best,
Paul
Paul Kopf Product Manager VSL