Hello. I deleted your duplicate post ("Strangest and weirdest error ever!!!!!!) as duplicate posts (in the words of our Site policy) only fragment[s] the support you receive and make[s] it more difficult for other users to find the correct information in the future when they do a search.
Also in future, please ensure your subject title also follows our Site policy:
Choose an informative subject line
Subject lines are like advertisements. You want helpful Moodlers with solutions to your specific problem to find and read more about your issue. Instead of using a subject line like "Urgent help needed!!!" use a subject line which is specific, such as, "Restore stops with error message 'xyz'".As for your assignments, it is perhaps because students have already submitted to the assignment that you cannot change it? Try making a new assignment and see if you can change it then.