That's because my service is registered with a virgin email address.
It's via mobile data or other external wifi networks that's the issue anyway as I don't use Virgin TV Go at home. By the way, Vigrin TV Go is working for my tablet and mobile phone, it's just not on my laptop - so it's surely a device issue.
I was last able to use it about 2 weeks ago now and haven't had this issue for nearly 2 years. Last time this happened I spent hours on the phone to get an answer and eventually was told that Virgin had had an outage and that eventually the TV Go service would work again. And it did eventually but months later.