We've had a copy of Guitar Hero On Tour: Decades for a while, and a review ready to go for a few weeks too. The trouble was that we wanted to test the multiplayer 'Share The Music' feature that lets you face off against another DS with the original On Tour game, and it just wasn't working.
Activision Australia today confirmed to us at Sliced Gaming that they had unwittingly shipped UK Decades cartridges that were incompatible with the AUS On Tour cartridges. No need to worry, though, folks - if you give customer service a ring, they'll swap it over for a compatible US version. Future shipments of the game will come with the US version in the box.