Any time I try to access the Account Bank, I get a message that goes something like "You cannot access the Account Bank at this time".
Initially, I thought it was because an Account Bank is used to share items between characters on one account. So, it might make sense to disable this if there aren't multiple characters on the account. But, I've since added a second character and still don't have access.
Is this some sort of special, subscribers-only feature? Usually these are denoted by some in-game mention of how the feature can be purchased, but I haven't noticed that in this case.