Jason, things got so convolution on my computer (UE problems) that I ended up having to reboot and I created new but like files in a new website. Enclosed are the files from that effort, which have the same results as I noted, i.e., form is not submitted. Only difference from my last entry is that the new file does not include the "die" or other added PHP code nor did I delete the validation behavior on the file form field.
Also, I notice that in the file where I created the form fields from within DW rather than FB, the enctype="multipart/form-data" information is automatically included in the form statement and that form is successfully submitted, i.e., I do get the "Thank You" page, as expected, after submitting the form and I get an email with the attachment.
Hope this helps, and thanks for sticking in there with me on this. I'm sure we are close to a solution.