by Mary Cooch.
Hello again
I can't see your screenshot very well but from what you say about once one student has submitted no others can submit, I am thinking you are perhaps using the group assignment feature but you don't have the "require all group members submit" setting enabled. Thus when one student submits then the assignment is considered complete and others don't need to submit
So you either need to have your assignments as individual assignments NOT group submissions, or to enable "require all group members submit"