Your personalized trainers are working fine on my machine. This means that something on your machine is blocking or interfering with the authentication process. Could be AV, firewall, download accelerator, etc. You can also try using an offline key, but the same program might block it as well.
With AV turned off, firewall turned off and no download accelerator installed, I still cannot access personalized trainers. I have also tried using an offline key with no success.
As far as I can recall, the problem started after I downloaded and installed Vista Service Pack 2.