I shortened an affiliate link. I did not like the characters, it looked messy. I shortened the same URL again and I got a neat set of characters this time.
I tested it , it worked.
Then I sent an email to 17,000 people and then suddenly it did not work. Probably because it has a short version already.
http://goo.gl/5X39f - this was it.
And then I had to send another email with the correct link.