Since the latest Kindle upgrade (Version 3.4.0.156) it's not working at all on my Viewpad. I've reported the fault to Kindle Support and they say the engineers are working on it but don't know when the fault will be fixed and I'm to be patient. 
If yours isn't working can you please report it to Kindle Support - the more of us that do so the better!
Until then I can't read the books that I've paid for!
If yours isn't working can you please report it to Kindle Support - the more of us that do so the better!
Until then I can't read the books that I've paid for!
