When you click the KB link you get a re-direct link which contains a built-in expiration code.
The link that I get when I click just now is:
cakewalk.s3.amazonaws.com/support/SONAR/SRX2/Downloads/SONARX2ProducerQuickFix.exe?AWSAccessKeyId=AKIAI43XBK2ZMSVE7TAA&Expires=1348932518&Signature=mgcWTrAC0HNJS5s4dTWNqRv3H%2bc%3d The Expires field is set with an expiration date that is in the 'near' future, so if you wait too long you will get an error.
If you change the expire field, you get a signature mismatch because that field encodes the URL.