diff -r 36a5a5113b94 tryton/health_calendar/health_calendar.py
--- a/tryton/health_calendar/health_calendar.py	Thu Jan 21 21:23:07 2016 +0700
+++ b/tryton/health_calendar/health_calendar.py	Fri Jan 22 22:48:03 2016 -0500
@@ -59,7 +59,8 @@
             if values['state'] == 'confirmed':
                 if values['healthprof']:
                     healthprof = Healthprof(values['healthprof'])
-                    if healthprof.name.internal_user.calendar:
+                    if (healthprof.name.internal_user and
+                            healthprof.name.internal_user.calendar):
                         patient = Patient(values['patient'])
                         appointment_date_end = None
                         if values.get('appointment_date_end'):
