I can login, but after closing the browser and logging in again I get the message "You are not allowed to login. Please check the name and password before trying to log on again."

Solution:

1. You are still logged in and probably closed the browser of the previous session using "close browser" cross of  IE. You will have to wait until your account is timed out (mostly approx. 10 minutes) or contact your super user to log out your account.
2. You mis-typed your companyname, username or password, check CAPS Lock if turned off and try to log on again.