Easy fix to a Poor Application Process UI

I have been working on a site lately that is trying to gain some revenue through referrals; it’s a pretty common tactic I have come to learn and I am anxious to see the results (if any). Naturally applying for an account with any of these companies requires the filling out of an online application form. One of these companies Commission Junction has a pretty simple but lengthy process which seems fine at first but they make an annoying mistake for non-US publishers. It’s an easy fix too.
In this screen shot you see that they require a tax id. But there is no instructional text provided as to what exactly I should put there (I don’t have a tax id). I put “Not Applicable”.
I then got an email with a rather confusing set of text telling that they only accept “those applicants that provide a valid tax identification number in the “Tax ID” field of their application”. Then they tell me that if I am not subject to US taxes, please leave the “Tax ID” field blank, and resubmit the application. The tone of the email sounds like it was written by a lawyer, instead of a human being concerned about doing business.
Instead of telling me of my error via email and forcing me to reapply how about designing the application process and form in such a way as to help mitigate errors. Here is a possible example.
A rough example - not to scale