I'm new at this and somehow managed to get a second artist into my tags (Abba\Abba) and I can't figure out how to delete it on 3,500+ files. Any ideas appreciated. Thanks.
Could you check for one of these files if you have "multivalue fields" for ARTIST?
For that select a file, press Alt-T to open the extended tags dialogue.
If you see the field ARTIST twice then you have them.
You can delete these duplicate fields with an action of the type "Remove duplicate fields".
Worked like a charm! Thank you very much!!