Hello,
Microsoft Security Advisory (2661254) - Update For Minimum Certificate Key Length to 1024 bits has caused us some grief due to some appliances (switches, routers, etc) that have a self signed cert of 512 bits. While we thought it was related to Java, we were mistaken. It turned out to be the change to force IE not to accept certs with key lengths less than 1024 bits. Unfortunately, IE wasn't too helpful in diagnosing the root cause of the issue. IE8 simply doesn't display any error, IE9 displays a prompt to continue but doesn't continue.
Hopefully this information can get back to the IE developer team in the hopes that there can be an update to provide a little more information to a user in IE's output when this issue is encountered.
Thanks,
Richard J C.