If someone enters their password incorrectly a few times, their Acuite account will be locked.   The account will need to be manually unlocked before they can attempt to log in again.

This can be done with someone with Admin permission rights within your company.  

Go to the System Settings menu and click Companies.

Find the relevant company in the list and click on the arrow on the right to expand the list.

Go to the user's name and click the Edit button.

Then click the Unlock User button and the Re-send Password email (because presumably the account has been locked because they've incorrectly entered their password a few times.  Then click Save.  This will unlock their account and send them the email, prompting them to set a new password.