To unlock a locked account, you need to run pam_tally2, which is a tool that keeps tracked of failed logins. Pam_tally2 is installed on most Linux systems. To unlock an account, just run the following commands:

pam_tally2 --user=ulysses --reset

Have the user login again. It should work.

Some systems might be using an older pam_tally. The command for that will be.

pam_tally --user=ulysses --reset=0