If a user enters their password incorrectly first time the will see Google reCAPTCHA on the login screen that they need to click to prove they are not a bot.

If they enter their password incorrectly five times within 15 minutes then they will see the message below on the login screen and their user ID will have been disabled.

Don't worry, as long as you have "admin" permissions you can log into your Hub and re-enable the user.

Step 1: Navigate to the Company page from the left navigation options. Here, in the Users tab, you will find your disabled colleague!

Step 2: Click into the user. 

Step 3: enable the user by moving the toggle (highlighted above) to enabled and then save your changes. The user will now be enabled!

Final step: ask your colleague to try again. As they had locked themselves out through an incorrect password it is probably worth them following the "i've forgotten my password" link on the login page to change their password, otherwise they may find themselves locked out again!