Inexplicable CSRF Error

I'm pulling my hair out trying to figure out why CI is not matching my CSRF token value. What else could cause this error? (error is equal to "old"). What does that mean? I've got a hidden csrf field and value in my view's form with method="post". Why would it not match the one CI is looking for? I've a zillion pages with forms like this. All of the others work as expected. Usually when I get the "The action you requested is not allowed" error is because I forgot to add 

PHP Code:

<?= csrf_field() ?>

Code:

Session User Data
__ci_last_regenerate 1726847150
_ci_previous_url https://dev-bnc4-web7.bsg.na.baesystems.com/user/otp/146/[email protected]
csrf_token_name a4cabeb296c28a07509bce759502297e
forgot_username 1
otp_errors 1
error The action you requested is not allowed.
__ci_vars
Array
(
    [error] => old

)

Simpler is always better