'Enter passphrase for key: xxxx.pem'

[Cryo-EM in the cloud]

What is happening when I get the following prompt when I'm trying to log into an Amazon EC2 instance using ssh? 

Enter passphrase for key: xxxx.pem

[Michael Cianfrocco]

This error shows up when there is a permissions issue (or any other problem) with the keypair. 

Make sure that the permissions for the keypair are correct: 

chmod 600 xxx.pem

We also saw this problem when the file keypair was corrupted (Firefox crashed as we were downloading the keypair). 

So, if you see this problem, just try remaking the keypair within Amazon and try again.