Index: lams_central/src/java/org/lamsfoundation/lams/authoring/ObjectExtractor.java
===================================================================
diff -u -r7132eb1ddde7a0b43e940678735cfd3eed63f60c -rd7ecd4ec0bd29174cd2385a51e3d276db8a3f7e9
--- lams_central/src/java/org/lamsfoundation/lams/authoring/ObjectExtractor.java	(.../ObjectExtractor.java)	(revision 7132eb1ddde7a0b43e940678735cfd3eed63f60c)
+++ lams_central/src/java/org/lamsfoundation/lams/authoring/ObjectExtractor.java	(.../ObjectExtractor.java)	(revision d7ecd4ec0bd29174cd2385a51e3d276db8a3f7e9)
@@ -1233,10 +1233,12 @@
     private void buildScheduleGateActivity(ScheduleGateActivity activity, ObjectNode activityDetails) {
 	activity.setGateStartTimeOffset(JsonUtil.optLong(activityDetails, AuthoringJsonTags.GATE_START_OFFSET));
 	activity.setGateEndTimeOffset(JsonUtil.optLong(activityDetails, AuthoringJsonTags.GATE_END_OFFSET));
-	activity.setGateActivityCompletionBased(
-		JsonUtil.optBoolean(activityDetails, AuthoringJsonTags.GATE_ACTIVITY_COMPLETION_BASED));
-	SystemTool systemTool = getSystemTool(SystemTool.SCHEDULE_GATE);
-	activity.setSystemTool(systemTool);
+	activity.setSystemTool(getSystemTool(SystemTool.SCHEDULE_GATE));
+	
+	Boolean isGateActivityCompletionBased = JsonUtil.optBoolean(activityDetails, AuthoringJsonTags.GATE_ACTIVITY_COMPLETION_BASED);
+	//check the previous activity is available as well
+	isGateActivityCompletionBased &= activity.getTransitionTo() != null;
+	activity.setGateActivityCompletionBased(isGateActivityCompletionBased);
     }
 
     private void createLessonClass(LessonClass lessonClass, ObjectNode groupingDetails) {
Index: lams_common/src/java/org/lamsfoundation/lams/learningdesign/strategy/ScheduleGateActivityStrategy.java
===================================================================
diff -u -r7475d08afc280b5e2e5ddf04e8bf35e3166aaf80 -rd7ecd4ec0bd29174cd2385a51e3d276db8a3f7e9
--- lams_common/src/java/org/lamsfoundation/lams/learningdesign/strategy/ScheduleGateActivityStrategy.java	(.../ScheduleGateActivityStrategy.java)	(revision 7475d08afc280b5e2e5ddf04e8bf35e3166aaf80)
+++ lams_common/src/java/org/lamsfoundation/lams/learningdesign/strategy/ScheduleGateActivityStrategy.java	(.../ScheduleGateActivityStrategy.java)	(revision d7ecd4ec0bd29174cd2385a51e3d276db8a3f7e9)
@@ -39,11 +39,10 @@
  * will be overiding the methods that defined in the abstract level.
  *
  * @author Jacky Fang
- * @since 2005-4-6
- * @version 1.1
- *
  */
 public class ScheduleGateActivityStrategy extends GateActivityStrategy {
+    private static final long serialVersionUID = -6702911163273937832L;
+
     public ScheduleGateActivityStrategy(GateActivity gateActivity) {
 	super(gateActivity);
     }
@@ -91,7 +90,6 @@
 	return super.shouldOpenGateFor(learner, expectedLearnerCount, waitingLearnerCount);
     }
 
-    @SuppressWarnings({ "unchecked" })
     public static Date getPreviousActivityCompletionDate(ScheduleGateActivity scheduleGate, User learner) {
 	Activity previousActivity = scheduleGate.getTransitionTo().getFromActivity();
 	if (previousActivity != null) {