First, in circumstances such as this it is always helpful to find out what the error message is, and to supply that message in your post.
Without it, anyone trying to help you is working blind. Not good.
That said, I have seen that there is a new vulnerability fix in todays Microsoft Windows updates. It addresses a flaw in the SSL/TLS handling routines which allows malicious third parties to force the connection from the latest SSL3 protocol down to SSL2. The advantage to them is that SSL2 uses weaker encryption - making it easier to break the cipher and read the stream contents. This would allow them to discover user names and passwords, and conduct "man in the middle" attacks by imitating your site content in various ways.
One (quite remote) possibility is that someone is attempting such an attack and your server has SSL 2 support switched off as a security measure.
Can you tell us more about the error message??
David