Once a user has been locked out of the system, changing their password won't unlock their account.
You can unlock a user by following these steps:

1. Select Subscription from the top right menu.
2. Select the "System Users" tab.

3. Find the user that needs to be unlocked in the list.
4. Click the unlock icon in the first column of the corresponding row.

5. Complete. The user will be able to login.