Index: app/ui/src/webapp/js/gradebook.js
===================================================================
--- app/ui/src/webapp/js/gradebook.js	(revision 126714)
+++ app/ui/src/webapp/js/gradebook.js	(working copy)
@@ -316,6 +316,11 @@
     var keepHighestVisibility = ""; // an unspecified display makes the column and column header visible
     var itemValueVisibility = "";
     var tbl  = document.getElementById(formName + ":categoriesTable");
+    if(tbl == undefined) {
+        // No categories
+        return;
+    }
+
     var thead = tbl.getElementsByTagName('thead');
     var header = thead.item(0);
     var headerRows = header.getElementsByTagName('th');