Maintenance for the week of March 25:
• [COMPLETE] ESO Store and Account System for maintenance – March 28, 9:00AM EDT (13:00 UTC) - 12:00PM EDT (16:00 UTC)
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.