Trying to do a full sync to existing engine DJ library but get this error? I can sync indiviual playlists no problem
Looks like there is a track with the same ID in there causing the problem. This might be a result from the recent Engine 4.2 changes I had to make to Lexicon.
If you have your entire library in Lexicon, the easiest fix is probably to delete your Engine library and then do a full sync. You will need to re-analyze your tracks in Engine though.
To delete the library, delete this folder: Music/Engine Library/Database2
Thank you for the speedy response @Christiaan 
I will do a backup and give that a go!