What I was getting at, is that sometimes the account lockout in 2005 seems to be a bit buggy.
I tend to see that if an account becomes locked out, just unlocking the account leads to it becoming locked again as soon as I unlock it and click "ok".
(And this isn't due to a user or service somewhere out there continuing to try to connect with the wrong password).
When I've seen this, and I've followed the route I described in my post above, this seems to resolve the issue.
Your issue sounded a bit like mine, but I was assuming that you were already happy that no-one was trying to connect using an incorrect password. If you're not satisfied that this is the case then yes, you need to track down where the bad login is originating from.
Good luck in getting this sorted.