When a teacher clicks Add assignment from the gradebook or New shared assignment from the Edit assignments page, the Add to grid is not editable. They are unable to click on New or to change the existing entries under Class ID, Student Date Due, Student Time Due or Category. All other fields are editable. This may only occur for certain teachers in certain classes or marking columns.
Download and install the latest patch, which contains all fixes from previous patches. If you are running an older version, download and install the latest version and then the patch.
Alternative solutions: Add the assignments through Gradebook, Edit Assignments for each class.
Remove all symbols or punctuation marks from Category names and Assignment names and descriptions for the affected class(es).