First, make sure you have BLS-2018 version 30.03.02 or newer installed.
The password for LeagueSecretary.com is now CAse SEnsITive. So most likely the issue is due to entering a password that does not match the letters and how they are UPPER or lower case. If needed, go to LeagueSecretary.com, log in, then change your password, noting the UPPER/lower case of your new password. Then come back to BLS-2018 and enter the new password.
You may also want to clear out the league ID, Username and Password and re-enter the information in again, double-checking the password.