I've not used Home v1 for years.... any reason why you still wnt to use it?
(I realise it's still needed for certain models and software-only versions)
I've still got it on my PC though - I rejected all efforts by Home 2 to delete it!
So I just ran it, and sure enough, I couldn't log in with an existing account name either. But I *was* able to create a new account.
So I think you either need to contact TT Customer Support and see what they say (probably just to install Home 2 !) or maybe you could create a new user name and move your device onto that new account? (careful though, if you have any map subscriptions on the old account)