You should tell the seller about your problem. I sent one yesterday that didn't open the first time (don't know why; it was the first time this had happened with one of my files that I know of) but when I re-sent it, it was fine. Sometimes I've had the experience where the customer's inbox is FULL, so it gets bounced back to me! If they let me know, we work it out (usually they just delete stuff from their full inboxes).
You could ask your seller to send the file through yousendit.com. It's free and easy, and you download the file from the website so it doesn't go through your e-mail.
If you still can't save it, I'd say it's time to look at how much space you have left on your computer! I had to move a whole year's worth of photos off, because I was running out of space.
Hope that helps!