Index: admin_list.py
===================================================================
--- admin_list.py	(revision 11434)
+++ admin_list.py	(working copy)
@@ -120,7 +120,7 @@
 
         th_classes = []
         new_order_type = 'asc'
-        if field_name == cl.order_field or admin_order_field == cl.order_field:
+        if cl.order_field != None and (field_name == cl.order_field or admin_order_field == cl.order_field):
             th_classes.append('sorted %sending' % cl.order_type.lower())
             new_order_type = {'asc': 'desc', 'desc': 'asc'}[cl.order_type.lower()]