I've just noticed that my account was having some login problems. It appears that something had changed in the way that the forum stored the password since it should have matched, but it didn't and I was rejected.
If anyone else has problems logging in then please try requesting a new password, logging in with the new password and then setting your password back to something you'll remember. Once you've done that and logged in then please PM me and tell me so that I know which accounts have had problems (e.g. old accounts).
Thanks, and sorry for any inconvenience caused.