@Royston-Vasey I had exactly the same problem and was unable to comment for well over a week. I reported it via email and through the live chat and they said they would get the maintenance team to look at it.
After a couple of days I tried logging into the Forum using my username instead of email address and this got me back in. Not sure if this was because the maintenance team had done something or not, as it still doesn't work if I use my email address. I'd try this if you haven't already, otherwise I'd give the live chat a go to report it to FI, as this was much quicker than email.