Never could get the attachment to go through even after setting the upload_tmp_dir value (host provider offered no other solutions), so it has been replaced with a simple mailto link. The attachment was being received on the server, but not attaching to the email. Very disappointed such a common form element wouldn't work.
Now, the form is no longer sending. On submit, the page comes back with a validation message that the checkbox hasn't been clicked, even though it has. You've fixed validation errors before, but I don't know what you did, or if it's related.