Hello, @Moin! 
Thanks for the report. Since the error message is thoroughly unhelpful it’s hard to say exactly what happened here, but I’ve gone over the code and found at least two things that can cause an error:
- The notice was already dismissed by another admin or in another tab.
- The user trying to dismiss isn’t an admin. (This can’t be the problem above, because the error is different.)
I have added fixes for these two cases this morning. I’ll leave this topic open for a while to see if it happens again. 