Maintenance for the week of July 27:
• NA megaservers for maintenance – July 27, 6:00AM EDT (10:00 UTC) -11:00AM EDT (15:00 UTC)
• EU megaservers for maintenance – July 27, 10:00 UTC (6:00AM EDT) - 15:00 UTC (11:00AM EDT)
You may just need to wait 10 to 20 minutes before logging in again. There are troubleshooting steps found here that can help if this login error continues.
If you have already tried power-cycling and opening ports, you should open a ticket with customer support for further help.