Hi Allison,
That error message comes up when we've not received anything from your payment processor yet. Sometimes it is because the payment is delayed, more often it can be the sign of a communication problem between the processor and our system, but according to your earlier posts you are giving out the file for free, so it would be going through our free checkout.... I'd guess offhand that there's a problem with the transaction number your IFRAME is trying to reference.
The big thing is that E-junkie is not a free download service, you don't even need to be going through all this trouble to give away a file to get people to sign up on your mailing list in the first place.
If you just want people to download a file for free then you can just upload the file to your Web site or any dedicated free file hosting service and make a link to it, just like you'd make a link from one page to another:
<a href="http://www.yoursite.com/path/to/yourfile.ext">Click here to download my file</a>
If you at least want to collect names/emails, but you still don't need to issue each person a unique link that expires, you could have a generic HTML contact form on your site that submits to any generic form-handler script, or even a subscription form for a mailing-list service like Aweber, which then leads to your free-download page after the form is submitted.
We're already providing unlimited bandwidth for downloads that result from sales, but bandwidth isn't free. In order to keep our costs low we have to have limits on the number of free checkouts/free download links any account can generate in a day. To avoid getting into a situation where someone tries to download your file through our cart but gets an error message/limit reached message instead we really recommend that you use other means to distribute your free files, while using our service for the ones you are selling.