Dates disappear on 'Edit'
Try looking at yoursite.ca/admin/build/themes/settings. 

When there, check that under "Display post information on" that your content type is checked.

After looking at this, it seems like a bug in the date module. Try updating the date module, but make sure that you have a backup of the site before doing so.

You should also soon upgrade to Drupal 7 or 8, as Drupal 6 sites risked being hacked.