I get an error when trying to SSH into a compute server. How do I fix it?

You'll need to carefully read the error message to determine where the problem is originating. A frequent problem that people have if they logged into a cluster node a long time ago, and then had a long period of not using that node (server), is that the SSH key for the host has changed in the interim. In a case like this, you'll get an error message like the following:

@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@ 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
1b:0e:5f:3b:e2:4e:bc:f4:ee:97:21:86:82:e4:90:47.
Please contact your system administrator.
Add correct host key in /Users/mpearrow/.ssh/known_hosts to get rid of this message.
Offending key in /Users/mpearrow/.ssh/known_hosts:73
RSA host key for mindhive has changed and you have requested strict checking.
Host key verification failed.
In a case like this, you simply need to edit your known_hosts file, which is usually found on your desktop or laptop home directory, in a hidden directory called .ssh (note the leading dot, which is what makes the directory normally invisible). Edit that file and remove any reference to the server that is complaining. The try SSH again; the problem should be fixed.