I'm just full of mistakes today.
Just fixed a small error where some members couldn't post, access their profile or PM box due to the Guild group being given Guest privileges. Those that could post where able to because they also where in another membergroup (such as Moderator, Extra Access, etc.) This only affected those in a guild and no other group.
It should be fixed now, I have two cases confirming it is. If you're still experiencing issues please let me know.