Can't enter grades in gradebook

[aburke]

Hi,

I have a strange problem.  Some of my students have stopped participating, although they are still registered in the class.  They are no longer completing quizzes and exams.  For some quizzes and exams I can enter a zero, but for others I cannot.  The space for their grade in gradebook is greyed out.  I have tried all kinds of ways to enter a  grade.  When I try "speedgrader" their name does not show up for that quiz/exa, when I try to just enter a "0" in gradebook, it won't let me.  For other quizzes and exams I can enter a "0" in gradebook.  I am also using Lockdown Browser with webcam with these quizzes.

Can anyone help with this?

Thanks!