Maintenance for the week of May 25:
• PC/Mac: No maintenance – May 25
• ESO Store and Account System for maintenance – May 27, 6:00AM EDT (10:00 UTC) - 4:00PM EDT (20:00 UTC)
I've used both - I prefer UserID but whichever you choose, be SURE to spell it right! In game, the capital i (I) and the lower case L (l) are as identical as they are in text here, and that can be a real problem, as are non-English characters.