Okay, after rereading your original post, I think I've realized what your friend's problem is:
Your friend might have registered for the Beta Forum back during the Beta test, but from what I can gather, he has not registered here on the Lodestone Forum - this is a completely different forum from the old Beta forum with separate accounts. Hence he doesn't have an actual Lodestone Forum account - if his FFXIV service account is active it's a simple matter to register (a forum account is tied to your FFXIV account), but the meat of it is, a Forum account is optional for players and hence has to be created manually. Participating in the Beta test doesn't grant access automatically either.
So yeah, tell your friend to sign up here on the Lodestone (it will ask him to login with his SE Account details as a part of the process), and then he should be able to start posting here.![]()