Dormant Accounts
Staff accounts become dormant when the user does not log in for 180 Days by default but this may have been changed in your school's Security Settings. Users that are 'Dormant' cannot log in even if they have the correct credentials until someone with admin access to MINTclass re-activates them.
Log into MINTclass with an admin account and go to Cortex - Main - Staff Admin
You will see Dormant Accounts on this screen. You can click on the Activate User icon and do each user individually if you wish but there is of course a quicker way. Scroll to the bottom of the screen and you will see the two buttons below.
Click on Select All Dormant Accounts and you will now see two new buttons at the bottom of the screen.
Click on Activate Selected Staff and you will get the Activation pop-up up which will allow you to re-activate staff as necessary.