So only lifetime members can register additional accounts?  This doesn't seem like a good idea at all.
I have experienced this same problem today trying to register a second account to my wallet.
We have been told that the only way to conceal our full balances is to have a separate anonymous account but can apparently only register an additional account if we are a lifetime member?  If so, this should be added to the membership information page as a perk of membership; it is much more significant than cash back on some fees.

That means you should get the account upgraded first to the lifetime member.

Then, you can register new accounts by the old account.

When trying to register a new account i keep getting the following error

fee_paying_account->is_lifetime_member():