Meanwhile , I went into Account details and it auto filled my steam and twitter ID (they were there when i clicked account details). When I clicked save I got an error that they were both in the wrong format.
Is it that the old forum format isn't compatable?
Ok it started off as: Aeronwen_Trewent
that got an error so I tried the whole url:
https://steamcommunity.com/id/Aeronwen_Trewent/
with and without the final slash
still an error
EDIT: Apparently it does not accept underscore anywhere in the name. So that is a feature I will not be using