Success! I ran the VST reset, and although initially VocALign came up again with the activate number having been used too many times, I just cancelled the dialogue and tried again, and it loaded, and is fully functional.
I am so grateful to everyone who helped me out here, blown away by help on this forum. Thank you so much.
Martyn

Enjoy!

When you have plugins using an iLok you should add them to the iLok BEFORE launching SONAR.
Otherwise once the scan runs and the authorization fails, the scanner will flag the plugin as "failed" and it will not try and scan it again by default. This is why SONAR won't see it.
While you can reset and rescan, the most painless way to get SONAR to see it again is to temporarily check the "rescan failed plugins" box in the VST preferences. The next time the scan runs it should reload the VST and try and authorize again.
This is the most common reason for plugins missing from SONAR.