my site will be selling downloadable PDFs only.

I thought I'd got everything set up correctly but when I did a test purchase, it said:
Not Available At This Time
Sorry, we are not shipping to your region at this time.
Please contact us for alternate arrangements.

How can I make it so that people don't need to register, but can if they want to - I'd like to make the prices a little higher for non-registered purchasers if possible, but that's not really important unless it's easy to set up.

My real problem is that I want people to be able to buy from the site and get a download link either on the site after paying with paypal, or in an email.

Is there a place where I can set the download link to expire in xx days or hours?

thanks.