There are some rare instances where Active Directory may mis-report an account as being expired or disabled when it isn’t, preventing them from logging in. If you encounter this condition then you can disable OVERLAPS’ internal checks for expired accounts by using the “Disable Account Expiry Checks” individual user menu action.
Note that if the account is actually properly disabled or expired in Active Directory then login will still fail, and this option should only be used as a last resort.