Thanks for the replies.
No Pro Channel fx, busses & all vi's removed from the project.
I was able to get the missing message stop however it was the order in which I deleted tracks, files & buses that made the difference.
Previously I always deleted the tracks-vi's first then the buses.
Then I tried deleting the buses first, then the vi's & tracks. The project then opened normally.
I also noticed that several missing plugins were reported to be on re-named tracks or buses. Example I renamed Snare RV to Room RV. The message reported was a missing plugin on the Snare RV bus (either way I deleted that bus anyway & would still get the message)
I don't remember if I used a user template but it's possible (I renamed the buses sometime back in 2011) I do recall template issues in the past so maybe that is related somehow.
I've opened older projects like this many times in newer versions of Sonar but never had this problem.
I have a feeling that Kontakt (several instances were used) might have done something 'weird' to the project
I wouldn't call this a bug but an isolated abnormality. Just wish I knew what caused it.
Thanks again.