When I turn on the calendar,  module I get  a huge warning list:
warning: Attempt to modify property of non-object in /var/www/drupal-6.19/sites/all/modules/calendar/includes/calendar_plugin_display_page.inc on line 47 through  line 167 then

warning: Attempt to modify property of non-object in /var/www/drupal-6.19/sites/all/modules/calendar/includes/calendar_plugin_display_page.inc on line 47.

warning: Attempt to modify property of non-object in /var/www/drupal-6.19/sites/all/modules/calendar/includes/calendar_plugin_display_attachment.inc on line 164.

If I turn Calendar off the errors disappear.

What am I doing wrong
Thanks
Roger