Up until yesterday, i could ssh to a remote system in my network.But now......

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@ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @
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IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!
Someone could be eavesdropping on you right now (man-in-the-middle attack)!
It is also possible that the RSA host key has just been changed.
The fingerprint for the RSA key sent by the remote host is
26:cd:d9:4d:f8:7e:14:27:a5:8b:0a:48:09:0e:a5:d2.
Please contact your system administrator.
Add correct host key in /root/.ssh/known_hosts to get rid of this message.
Offending key in /root/.ssh/known_hosts:2
RSA host key for ppgp1 has changed and you have requested strict checking.
Host key verification failed.



Host and remote OS : knoppix linux. How can I resolve this?