An odd 'wrong' notice.
I got this odd 'wrong' notice while doing a Welsh exercise. I posted it in the Welsh discussion forum, and I was advised to post it in the Troubleshooting forum, as well.
My answer is identical to the one suggested by Duolingo, except for the capitalized first letter, which in other exercises is never an issue (had it been so, it would have been marked as a typo, but the answer would have been accepted).
It took Duolingo quite a while before showing me the notice, about 60 seconds, as if something was not working well with the database.
I was unable to report the problem using the 'Report a problem' form, because it does not include this particular case.
I got two of theese yesterday during the reported glitch. Your post is 3 days old when according to the status page there was no glitch. But I don't really believe them, in the past week I hade not once problem with duolingo around 19:00 UTC (eg. discussions page loading very slowly or not at all).