problem at login web authentication

Hi, I cannot log in with the default data admin/admin

http://isc.unsaac.edu.pe/cuscontest/public/login.php

but when I do this through curl it seems to be working fine: curl --data "login=admin&passwd=admin&cmd=login" http://isc.unsaac.edu.pe/cuscontest/public/login.php

what could be the reason for this behaviour, hope you can help me.

BTW it was working fine before, I cannot realize why it suddenly took this behaviour, the domjudge version is 4.0.5 and I'm using this version of ubuntu. ubuntu@ip-172-31-28-85:~/domjudge-4.0.5$ lsb_release -a No LSB modules are available. Distributor ID: Ubuntu Description: Ubuntu 14.04.2 LTS Release: 14.04 Codename: trusty ubuntu@ip-172-31-28-85:~/domjudge-4.0.5$