I always do the 90 day reporting online without problems. I recently left the country for a weeks holiday and returned on the 4th March. I think the 90 report is reset at this date, yet last week I got an email reminder to do the report, so I did an online report and it has been rejected. I presume this is because my 90 day is reset and I need to do again around 10-15days before the 4th June. Can anyone just clarify this to save me a trip to check at immigration.
TLDR : Answer Summary
The 90 day reporting period resets on the date you re-enter Thailand, with your arrival date counted as day one. Therefore, after returning on 4th March, your next report should be due around 4th June, making the email reminder you received irrelevant.