Index: app/models/mailer.rb
===================================================================
--- app/models/mailer.rb	(revision 3818)
+++ app/models/mailer.rb	(working copy)
@@ -321,7 +321,7 @@
                                           :conditions => s.conditions
                                     ).group_by(&:assigned_to)
     issues_by_assignee.each do |assignee, issues|
-      deliver_reminder(assignee, issues, days) unless assignee.nil?
+      deliver_reminder(assignee, issues, days) if assignee && assignee.active?
     end
   end