diff --git a/lib/ajax/ajaxcourse.js b/lib/ajax/ajaxcourse.js
index b29a25024e0..0e5dd3421da 100644
--- a/lib/ajax/ajaxcourse.js
+++ b/lib/ajax/ajaxcourse.js
@@ -62,6 +62,7 @@ function main_class() {
     this.courseformat = null;
     this.marker = null;
     this.numsections = null;
+    this.lastsection = null; // real last section num including unavailable
 
     //things to process onload
     onloadobj.add('main.process_document();');
@@ -118,11 +119,11 @@ main_class.prototype.process_document = function() {
     //process sections
     //var ct = 0;
     //while (document.getElementById('section-'+ct) != null) {
-    var maxct = this.portal.numsections;
     this.courseformat = this.portal.courseformat;
-    for(var ct=0; ct <= maxct; ct++){
-        if(document.getElementById('section-'+ct) != null) {
-            this.sections[ct] = new section_class('section-'+ct, "sections", null, ct!=0?true:false);
+    for(var ct=0; ct <= this.portal.lastsection; ct++){
+        if (document.getElementById('section-'+ct) != null) {
+            var dragable = ((ct > 0) && (ct <= this.portal.numsections));
+            this.sections[ct] = new section_class('section-'+ct, "sections", null, dragable);
             this.sections[ct].addToGroup('resources');
             if (ct > 0) {
                 var sectiontitle = YAHOO.util.Selector.query('#section-'+ct+' h3.weekdates')[0];
@@ -130,6 +131,8 @@ main_class.prototype.process_document = function() {
                     this.sectiondates[ct] = sectiontitle.innerHTML;
                 }
             }
+        } else {
+            this.sections[ct] = null;
         }
         //ct++;
     }
@@ -165,6 +168,7 @@ main_class.prototype.get_section_index = function(el) {
             return i;
         }
     }
+    return -1;
 };
 
 main_class.prototype.mk_button = function(tag, imgSrc, text, attributes, imgAttributes) {
diff --git a/lib/ajax/ajaxlib.php b/lib/ajax/ajaxlib.php
index dbbf55435f8..fdfb4927e1f 100644
--- a/lib/ajax/ajaxlib.php
+++ b/lib/ajax/ajaxlib.php
@@ -118,7 +118,7 @@ class jsportal {
      * Prints the JavaScript code needed to set up AJAX for the course.
      */
     function print_javascript($courseid, $return=false) {
-        global $CFG, $USER, $OUTPUT, $COURSE;
+        global $CFG, $USER, $OUTPUT, $COURSE, $DB;
 
         $blocksoutput = $output = '';
         for ($i=0; $i<count($this->blocks); $i++) {
@@ -138,6 +138,7 @@ class jsportal {
         $output .= "    main.portal.strings['marker']='".get_string('markthistopic', '', '_var_')."';\n";
         $output .= "    main.portal.strings['marked']='".get_string('markedthistopic', '', '_var_')."';\n";
         $output .= "    main.portal.numsections = ".$COURSE->numsections.";\n";
+        $output .= "    main.portal.lastsection = ".$DB->get_field_sql("SELECT MAX(section) FROM {course_sections} WHERE course = ?", array($courseid)).";\n"; // needed for orphaned activities in unavailable sections
         $output .= "    main.portal.strings['hide']='".get_string('hide')."';\n";
         $output .= "    main.portal.strings['hidesection']='".get_string('hidesection', '', '_var_')."';\n";
         $output .= "    main.portal.strings['show']='".get_string('show')."';\n";
diff --git a/lib/ajax/section_classes.js b/lib/ajax/section_classes.js
index f2a828eb5e6..ee79949bbb2 100755
--- a/lib/ajax/section_classes.js
+++ b/lib/ajax/section_classes.js
@@ -77,6 +77,11 @@ section_class.prototype.init_section = function(id, group, config, isDraggable)
 
 
 section_class.prototype.init_buttons = function() {
+    if (this.sectionId > main.portal.numsections) {
+        // no need to do anything in orphaned sections
+        return;
+    }
+
     var commandContainer = YAHOO.util.Dom.getElementsByClassName('right',null,this.getEl())[0];
 
     //clear all but show only button
@@ -92,7 +97,7 @@ section_class.prototype.init_buttons = function() {
         commandContainer.appendChild(highlightbutton);
         this.highlightButton = highlightbutton;
     }
-    if (this.sectionId > 0 ) {
+    if (this.sectionId > 0) {
         var viewbutton = main.mk_button('div', main.portal.icons['hide'], main.getString('hidesection', this.sectionId),
                 [['title', main.portal.strings['hide'] ]]);
         YAHOO.util.Event.addListener(viewbutton, 'click', this.toggle_hide, this,true);
@@ -150,7 +155,14 @@ section_class.prototype.process_section = function() {
         var resource = this.resources_ul.getElementsByTagName('li')[i];
         this.resources[this.resources.length] = new resource_class(resource.id, 'resources', null, this);
     }
-    this.summary = YAHOO.util.Dom.getElementsByClassName('summary', null, this.getEl())[0].firstChild.data || '';
+
+    var sum = YAHOO.util.Dom.getElementsByClassName('summary', null, this.getEl());
+    if (sum[0]) {
+        this.summary = sum[0].firstChild.data || '';
+    } else {
+        // orphaned activities
+        this.summary = null;
+    }
 };
 
 
@@ -205,6 +217,14 @@ section_class.prototype.move_to_section = function(target) {
     var oIndex = main.get_section_index(this);
     var tIndex = main.get_section_index(target);
 
+    if (oIndex == -1) {
+        // source must exist
+        return;
+    }
+    if (tIndex == -1) {
+        // target must exist
+        return;
+    }
     if (this.debug) {
         YAHOO.log("original is at: "+oIndex+" target is at:"+tIndex+" of "+(sectionCount-1));
     }
@@ -257,8 +277,17 @@ section_class.prototype.move_to_section = function(target) {
 section_class.prototype.swap_with_section = function(sectionIn) {
     var tmpStore = null;
 
-    thisIndex = main.get_section_index(this);
-    targetIndex = main.get_section_index(sectionIn);
+    var thisIndex = main.get_section_index(this);
+    var targetIndex = main.get_section_index(sectionIn);
+    if (thisIndex == -1) {
+        // source must exist
+        return;
+    }
+    if (targetIndex == -1) {
+        // target must exist
+        return;
+    }
+
     main.sections[targetIndex] = this;
     main.sections[thisIndex] = sectionIn;
 
@@ -286,6 +315,11 @@ section_class.prototype.swap_with_section = function(sectionIn) {
 
 
 section_class.prototype.toggle_hide = function(e,target,superficial) {
+    if (this.sectionId > main.portal.numsections) {
+        // no need to do anything in orphaned sections
+        return;
+    }
+
     var strhide = main.portal.strings['hide'];
     var strshow = main.portal.strings['show'];
     if (this.hidden) {