Why we are getting a PCI :: Error During Transaction message on one of our forms?

We are getting a PCI :: Error During Transaction message on one of our forms. The form is OLI - Luncheon for Life 2017. I have verified the Authorize.net connection and it is appearing on the website fine so I don't believe it is the script placed into Wordpress. I am out of ideas on what could be causing the issue. Please help. 

The PCI error "This transaction cannot be accepted" may be related to the incorrect transaction key on your account. Can you check if all the characters are entered properly? Please also check if the transaction key that you have is a live one and not a sandbox/test account.

If in case you have the correct transaction key but the submission still fails, you can generate a new Transaction key.

To obtain the Transaction Key:

1) Log into your Merchant Interface at https://account.authorize.net.

2) Click Account from the main toolbar.

3) Click Settings in the main left-side menu.

4) Click API Credentials & Keys.

5) Enter your Secret Answer (the answer to your Secret Question configured at account setup).

6) Select New Transaction Key.

To disable the old Transaction Key, click the check box labeled Disable Old Transaction Key Immediately.

(Note: If the Disable Old Transaction Key Immediately check box is not selected, the old transaction key will automatically expire in 24 hours.)

Click Submit to continue. Your new Transaction Key is displayed.

Please be sure to have your API Login ID and Transaction Key set in your Auth.net payment field.

If you're still experiencing this issue, please let us know.

Thank you!