diff --git a/app/models/observer/ticket/notification.rb b/app/models/observer/ticket/notification.rb
index b3bc869b8..f07afc9da 100644
--- a/app/models/observer/ticket/notification.rb
+++ b/app/models/observer/ticket/notification.rb
@@ -17,10 +17,20 @@ class Observer::Ticket::Notification < ActiveRecord::Observer
       # get current state of objects
       if event[:name] == 'Ticket::Article'
         article = Ticket::Article.lookup( :id => event[:id] )
+
+        # next if article is already deleted
+        next if !article
+
         ticket  = article.ticket
-      else
+      elsif event[:name] == 'Ticket'
         ticket  = Ticket.lookup( :id => event[:id] )
+        
+        # next if ticket is already deleted
+        next if !ticket
+
         article = ticket.articles[-1]
+      else
+        raise "unknown object for notification #{event[:name]}"
       end
 
       # send new ticket notification to agents
diff --git a/test/unit/twitter_test.rb b/test/unit/twitter_test.rb
index ee9fee0a9..e14d47807 100644
--- a/test/unit/twitter_test.rb
+++ b/test/unit/twitter_test.rb
@@ -150,7 +150,7 @@ class TwitterTest < ActiveSupport::TestCase
       text,
     )
     assert( dm, "dm with ##{hash} created" )
-    sleep 20
+    sleep 10
 
     # fetch check system account
     Channel.fetch