@ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
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

Please contact your system administrator.
Add correct host key in /home/username/.ssh/known_hosts to get rid of this message.
Offending key in /home/username/.ssh/known_hosts:17
RSA host key for ####### has changed and you have requested strict checking.
Host key verification failed.

What do I do? Please help.

It is saying you have an offending key in your known_hosts file. Did that server get restored? If so the key will be different, if not, then you might have a man in the middle attack.

What you can do is either put the new key in, or delete line 17 and it will ask you if you want to save the new one.

HTH