Invalid certificate authority signature
The certificate chain presented by rsi.hotmail.com does not have a valid digital signature from the Certificate Authority from which it claims to have a signature.
Leave pidgin running and eventually it will ask you to accept the new certificate - thats what i did this time - the previous time on my other install i installed a whole bunch of certificates via yast2 and that worked also
The general mechanism of key verification process behind private key/public key encryption is that when you receive a digital certificate containing the public key from a server, the root of the key chain contained in the certificate should match with one of the root keys stored in your machine. If no match is found, your machine can not determine if the server is genuine or not.