diff -Naur moodle_old//mod/assignment/lib.php moodle_latest//mod/assignment/lib.php
--- moodle_old//mod/assignment/lib.php	2012-03-16 05:34:53.000000000 +0530
+++ moodle_latest//mod/assignment/lib.php	2012-03-28 00:33:02.000000000 +0530
@@ -228,14 +228,26 @@
 
         echo $OUTPUT->box_start('generalbox boxaligncenter', 'dates');
         echo '<table>';
+	if(!$this->assignment->timeavailable && $this->assignment->timedue){
+	echo '</table>';		
+ 		print_error('Time Available Must be defined','assignment');
+	}
+	else{
         if ($this->assignment->timeavailable) {
-            echo '<tr><td class="c0">'.get_string('availabledate','assignment').':</td>';
+	    if($this->assignment->timeavailable > $this->assignment->timedue){
+		echo '</table>';		
+ 		print_error('invalidduedate','assignment');
+	    }
+	   else{
+	     echo '<tr><td class="c0">'.get_string('availabledate','assignment').':</td>';
             echo '    <td class="c1">'.userdate($this->assignment->timeavailable).'</td></tr>';
+	   }
         }
         if ($this->assignment->timedue) {
             echo '<tr><td class="c0">'.get_string('duedate','assignment').':</td>';
             echo '    <td class="c1">'.userdate($this->assignment->timedue).'</td></tr>';
         }
+}
         echo '</table>';
         echo $OUTPUT->box_end();
     }