Duplicating Action, what am I doing wrong?

Firstly sorry I know this is covered in the FAQ but I can't get it to work and can not figure out why.

Basically my jukebox software wants to use 'album artist' rather than 'artist' so I need to copy the artist tags into the album artist section. I've read the FAQ about using the format value action:

Action type: Format value
Field: BAND
Formatstring: %album artist%

So I've highlighted the mp3's that need an album artist tag.
click on Actions (quick), can't find format value on the actions icon.
Select Format Value
Field: ALBUM ARTIST
Format String: %artist%

It then does its little scroll through and tells me nothing has changed. If anyone can suggest what I'm doing wrong it will save me a huge headache and I'm sure a lot of wasted time.

Thanks

Sorry for the dumb question, it never clicked that to change the 'album artist' tags I had to actually enter BAND I thought that was just an example . Anyway sorted now.