[Closed] Google Apps Inventor - any users out there?

I realise starting a geek thread on the evening that al-Megrahi buys the farm is a hiding to nothing, but here goes...

I'm trying to set up Google App Inventor on my laptop. Downloaded and installed the latest version of Java (1.7) and the AppInventor setup which I think is the BlocksEditor for the local machine.

I can assemble some App components in the browser without any problems, but whenever I click on "Open the blocks editor" it hangs. I get a .jlnp prompt from the browser which is fine. Allowing that will launch Java which then tries to download the BlocksEditor. Which I've already installed....

Grrr....

Any ideas what I'm doing wrong? No obvious solution in FAQs and Troubleshooting pages.

Cheers,
SC