I got it to work! After lots of playing around the following seemed to to the trick.
All I did was 'install' Popcorn 4. Now I don't have a license for Popcorn 4 (I only have one for 3) but although I cannot run Popcorn 4 it did update my Toast Video player to Ver 3.0 (from Ver 1.0 that came with Popcorn 3)
I then started my Tivo Beta 4 and clicked play on the show I wanted.
Hope it works for you!