diff --git a/mozilla/calendar/base/content/calendar-event-dialog.js b/mozilla/calendar/base/content/calendar-event-dialog.js
index e83cb4dabae..f0a6abd9e27 100644
--- a/mozilla/calendar/base/content/calendar-event-dialog.js
+++ b/mozilla/calendar/base/content/calendar-event-dialog.js
@@ -78,10 +78,6 @@ function onLoad()
     // update the accept button
     updateAccept();
 
-    // disabling recurring todo until bug 328197 is fixed
-    if (isToDo(window.calendarItem))
-        disableElement("item-recurrence");
-
     // update datetime pickers
     updateDueDate();
     updateEntryDate();
@@ -243,6 +239,9 @@ function loadDialog(item)
         setElementValue("item-recurrence", "true", "disabled");
         setElementValue("set-recurrence", "true", "disabled");
         setElementValue("item-calendar", "true", "disabled");
+
+        // don't allow to revoke the entrydate of recurring todo's.
+        disableElement("todo-has-entrydate");
     } else if (item.recurrenceInfo)
         setElementValue("item-recurrence", "true", "checked");
 
@@ -295,6 +294,10 @@ function saveDialog(item)
             jsDateToDateTime(getElementValue("todo-entrydate")) : null;
         if (entryDate) {
             entryDate = entryDate.getInTimezone(kDefaultTimezone);
+        } else {
+            // no entrydate, no recurrence
+            item.recurrenceInfo = null;
+            window.recurrenceInfo = null;
         }
         setItemProperty(item, "entryDate",   entryDate);
 
@@ -486,14 +489,13 @@ function onEndTimeChange()
 }
 function updateAccept()
 {
+    var enableAccept = true;
+
     var kDefaultTimezone = calendarDefaultTimezone();
-    var acceptButton = document.getElementById("calendar-event-dialog").getButton("accept");
 
     var title = getElementValue("item-title");
     if (title.length == 0)
-        acceptButton.setAttribute("disabled", "true");
-    else if (acceptButton.getAttribute("disabled"))
-        acceptButton.removeAttribute("disabled");
+        enableAccept = false;
 
     // don't allow for end dates to be before start dates
     var startDate;
@@ -524,14 +526,21 @@ function updateAccept()
             jsDateToDateTime(getElementValue("todo-entrydate")) : null;
         endDate = getElementValue("todo-has-duedate", "checked") ? 
             jsDateToDateTime(getElementValue("todo-duedate")) : null;
+        
+        var taskRepeatWarning = document.getElementById("task-repeat-warning");
+        if (!startDate && getElementValue("item-recurrence", "checked")) {
+            enableAccept = false;
+            taskRepeatWarning.removeAttribute("hidden");
+        } else {
+            taskRepeatWarning.setAttribute("hidden", "true");
+        }
     }
 
     var timeWarning = document.getElementById("end-time-warning");
     if (endDate && startDate && endDate.compare(startDate) == -1) {
-        acceptButton.setAttribute("disabled", "true");
+        enableAccept = false;
         timeWarning.removeAttribute("hidden");
     } else {
-        acceptButton.removeAttribute("disabled");
         timeWarning.setAttribute("hidden", "true");
     }
 
@@ -541,12 +550,20 @@ function updateAccept()
     document.getElementById("read-only-cal").setAttribute("hidden", 
                                               !cal.readOnly);
     if (gReadOnlyMode || cal.readOnly) {
-        acceptButton.setAttribute("disabled", "true");
+        enableAccept = false;
     }
 
     if (!updateTaskAlarmWarnings()) {
-        acceptButton.setAttribute("disabled", "true");
+        enableAccept = false;
     }
+    
+    var acceptButton = document.getElementById("calendar-event-dialog").getButton("accept");
+    if (!enableAccept) {
+        acceptButton.setAttribute("disabled", "true");
+    } else if (acceptButton.getAttribute("disabled")) {
+        acceptButton.removeAttribute("disabled");
+    }
+    
     return;
 }
 
@@ -639,6 +656,8 @@ function updateRecurrence()
     } else {
         setElementValue("set-recurrence", "true", "disabled");
     }
+
+    updateAccept();
 }
 
 var prevAlarmItem = null;
@@ -691,6 +710,21 @@ function editRecurrence()
     args.calendarEvent = window.calendarItem;
     args.recurrenceInfo = window.recurrenceInfo || args.calendarEvent.recurrenceInfo;
 
+    var kDefaultTimezone = calendarDefaultTimezone();
+    if (isEvent(window.calendarItem)) {
+        var startDate = jsDateToDateTime(getElementValue("event-starttime")).getInTimezone(kDefaultTimezone);
+        if (getElementValue("event-all-day", "checked")) {
+            startDate.isDate = true;
+            startDate.normalize();
+        }
+        args.startDate = startDate;
+    } else if (isToDo(window.calendarItem)) {
+        if (!getElementValue("todo-has-entrydate", "checked")) {
+            return;
+        }
+        args.startDate = jsDateToDateTime(getElementValue("todo-entrydate")).getInTimezone(kDefaultTimezone);
+    }
+
     var savedWindow = window;
     args.onOk = function(recurrenceInfo) {
         savedWindow.recurrenceInfo = recurrenceInfo;
diff --git a/mozilla/calendar/base/content/calendar-event-dialog.xul b/mozilla/calendar/base/content/calendar-event-dialog.xul
index edc1f69915d..21c3b5e385e 100644
--- a/mozilla/calendar/base/content/calendar-event-dialog.xul
+++ b/mozilla/calendar/base/content/calendar-event-dialog.xul
@@ -137,6 +137,8 @@
             </hbox>
             <label id="end-time-warning" class="warning-text-class"
                    value="&newevent.endtime.warning;"/>
+            <label id="task-repeat-warning" class="warning-text-class"
+                   value="&newtodo.repeatstart.warning;" hidden="true"/>
           </vbox>
         </row>
 
diff --git a/mozilla/calendar/base/content/calendar-recurrence-dialog.js b/mozilla/calendar/base/content/calendar-recurrence-dialog.js
index 04458859d43..e7e1b56710b 100644
--- a/mozilla/calendar/base/content/calendar-recurrence-dialog.js
+++ b/mozilla/calendar/base/content/calendar-recurrence-dialog.js
@@ -43,6 +43,7 @@ function onLoad()
     window.onAcceptCallback = args.onOk;
     window.calendarEvent = args.calendarEvent;
     window.originalRecurrenceInfo = args.recurrenceInfo;
+    window.startDate = args.startDate;
 
     loadDialog();
 
@@ -82,34 +83,34 @@ function loadDialog()
     var props = sbs.createBundle("chrome://calendar/locale/dateFormat.properties");
 
     // Set label to '15th day of the month'
-    var nthstr = props.GetStringFromName("ordinal.suffix."+window.calendarEvent.startDate.day);
-    var str = props.formatStringFromName("recurNthDay", [window.calendarEvent.startDate.day, nthstr], 2);
+    var nthstr = props.GetStringFromName("ordinal.suffix."+window.startDate.day);
+    var str = props.formatStringFromName("recurNthDay", [window.startDate.day, nthstr], 2);
     document.getElementById("monthly-nth-day").label = str;
 
     // Set label to 'second week of the month'
-    var monthWeekNum = Math.floor(window.calendarEvent.startDate.day / 7) + 1;
+    var monthWeekNum = Math.floor(window.startDate.day / 7) + 1;
     nthstr = props.GetStringFromName("ordinal.name."+monthWeekNum);
-    var daystr = props.GetStringFromName("day."+(window.calendarEvent.startDate.weekday+1)+".name");
+    var daystr = props.GetStringFromName("day."+(window.startDate.weekday+1)+".name");
     str = props.formatStringFromName("recurNthWeek", [nthstr, daystr], 2);
     document.getElementById("monthly-nth-week").label = str;
 
     // Set two values needed to create the real rrule later
-    document.getElementById("monthly-nth-week").day = window.calendarEvent.startDate.weekday;
+    document.getElementById("monthly-nth-week").day = window.startDate.weekday;
     document.getElementById("monthly-nth-week").week = monthWeekNum;
 
     // If this is the last friday of the month, set label to 'last friday of the month'
     // (Or any other day, ofcourse.) Otherwise, hide last option
-    var monthLength = window.calendarEvent.startDate.endOfMonth.day;
-    var isLastWeek = (monthLength - window.calendarEvent.startDate.day) < 7;
+    var monthLength = window.startDate.endOfMonth.day;
+    var isLastWeek = (monthLength - window.startDate.day) < 7;
     document.getElementById("monthly-last-week").hidden = !isLastWeek;
-    var isLastDay = (monthLength == window.calendarEvent.startDate.day);
+    var isLastDay = (monthLength == window.startDate.day);
     document.getElementById("monthly-last-day").hidden = !isLastDay;
     if (isLastWeek) {
         str = props.formatStringFromName("recurLast", [daystr], 1);
         document.getElementById("monthly-last-week").label = str;
     }
 
-    document.getElementById("monthly-last-week").day = window.calendarEvent.startDate.weekday;
+    document.getElementById("monthly-last-week").day = window.startDate.weekday;
 
     if (!window.originalRecurrenceInfo)
         return;
@@ -243,7 +244,7 @@ function saveDialog()
         var recurtype = getElementValue("monthly-type");
         switch (recurtype) {
           case "nth-day":
-            recRule.setComponent("BYMONTHDAY", 1, [window.calendarEvent.startDate.day]);
+            recRule.setComponent("BYMONTHDAY", 1, [window.startDate.day]);
             break;
           case "nth-week":
             var el = document.getElementById('monthly-nth-week');
diff --git a/mozilla/calendar/base/public/calITodo.idl b/mozilla/calendar/base/public/calITodo.idl
index c3b79db6d58..32657dde8d0 100644
--- a/mozilla/calendar/base/public/calITodo.idl
+++ b/mozilla/calendar/base/public/calITodo.idl
@@ -94,5 +94,12 @@ interface calITodo : calIItemBase
   // IN-PROCESS.)  It's not clear that we want any more magic than a simple
   // property to control "all complete" vs "not complete in any way".
   attribute boolean isCompleted;
+
+  /**
+   * The duration of the todo, which is defined as dueDate - entryDate.
+   * Please note that null is returned if either entryDate or
+   * dueDate don't exist.
+   */
+  readonly attribute calIDuration duration;
 };
 
diff --git a/mozilla/calendar/base/src/calRecurrenceInfo.js b/mozilla/calendar/base/src/calRecurrenceInfo.js
index e89fdef1601..d6d9fe3698b 100644
--- a/mozilla/calendar/base/src/calRecurrenceInfo.js
+++ b/mozilla/calendar/base/src/calRecurrenceInfo.js
@@ -358,7 +358,13 @@ calRecurrenceInfo.prototype = {
                                          }
 
                                          // is our end date within the range?
-                                         var dtend = ex.item.getProperty("DTEND");
+                                         var name = "DTEND";
+                                         if (ex.item instanceof Components.interfaces.calITodo)
+                                            name = "DUE";
+                                         var dtend = ex.item.getProperty(name);
+                                         if (!dtend)
+                                            return;
+                                         
                                          if ((!aRangeStart || aRangeStart.compare(dtend) <= 0) &&
                                              (!aRangeEnd || aRangeEnd.compare(dtend) > 0))
                                          {
@@ -471,7 +477,12 @@ calRecurrenceInfo.prototype = {
         var proxy = this.getExceptionFor(aRecurrenceId, false);
         if (!proxy) {
             var duration = null;
-            if (this.mBaseItem.hasProperty("DTEND"))
+            
+            var name = "DTEND";
+            if (this.mBaseItem instanceof Components.interfaces.calITodo)
+                name = "DUE";
+                
+            if (this.mBaseItem.hasProperty(name))
                 duration = this.mBaseItem.duration;
 
             proxy = this.mBaseItem.createProxy();
@@ -480,7 +491,7 @@ calRecurrenceInfo.prototype = {
             if (duration) {
                 var enddate = aRecurrenceId.clone();
                 enddate.addDuration(duration);
-                proxy.setProperty("DTEND", enddate);
+                proxy.setProperty(name, enddate);
             }
             if (!this.mBaseItem.isMutable)
                 proxy.makeImmutable();
@@ -678,6 +689,17 @@ calRecurrenceInfo.prototype = {
     // in case we're about to modify a parentItem (aka 'folded' item), we need
     // to modify the recurrenceId's of all possibly existing exceptions as well.
     onStartDateChange: function (aNewStartTime, aOldStartTime) {
+
+        // passing null for the new starttime would indicate an error condition,
+        // since having a recurrence without a starttime is invalid.
+        if (!aNewStartTime) {
+            throw Components.results.NS_ERROR_INVALID_ARG;
+        }
+    
+        // no need to check for changes if there's no previous starttime.
+        if (!aOldStartTime) {
+            return;
+        }
     
         // convert both dates to UTC since subtractDate is not timezone aware.
         aOldStartTime = aOldStartTime.getInTimezone("UTC");
diff --git a/mozilla/calendar/base/src/calTodo.js b/mozilla/calendar/base/src/calTodo.js
index 5123d7335ba..45570b8b88e 100644
--- a/mozilla/calendar/base/src/calTodo.js
+++ b/mozilla/calendar/base/src/calTodo.js
@@ -159,6 +159,14 @@ calTodo.prototype = {
         }
     },
 
+    get duration() {
+        if (!this.entryDate)
+            return null;
+        if (!this.dueDate)
+            return null;
+        return this.entryDate.subtractDate(this.dueDate);
+    },
+
     get recurrenceStartDate() {
         return this.entryDate;
     },