Submitting subscribers to AWeber via a server-side script (PHP, ASP, ColdFusion, etc.) is not permitted. This also applies to any membership software or server-side shopping cart software that you may have installed on your site.
AWeber's API As A Replacement
AWeber boasts an API with the ability to add subscribers to your account in a way that will allow us to maintain a verifiable audit trail. As long as you are adding subscribers with their knowledge and consent, you should be able to do so using the API. You can create a developer account and learn more about it over at AWeber Labs.
Why Can't I Script Submissions Without Using The API?
Whenever a subscriber adds to your list, we need to establish an electronic Audit Trail for that subscriber.
The audit trail is necessary to prove to ISPs that the subscriber did come to you and request your information. It helps us to ensure the best possible deliverability for your — and all of our customers' — messages.
When a third-party script attempts to add subscribers (by forwarding generated information), we are unable to establish that audit trail, because we are not collecting subscriber information firsthand. Because of that, accepting subscribers from a third-party form or script would pose a risk to our ability to get your — and all customers' — messages delivered.
If we couldn't get messages delivered, we couldn't stay in business. We like staying in business. So, we don't allow subscribers to be posted to AWeber from third-party forms or server-side scripts.
What Can I Do Instead?
As mentioned above, you may be able to replace the script you are using with an app created to work with AWeber's API. Alternately, when subscribers fill out the AWeber sign up form, you can have it pass the information that they enter in it to your Thank-You page.
In addition to being a great way to personalize your Thank-You page, this offers you the opportunity to capture that information in your own local database, or do whatever else you need with it at that time.