What causes the error "Call-time pass-by-reference has been deprecated?"
The cause of the "Call-time pass-by-reference has been deprecated in
 _registry_check_code()" is a file that holds a class being loaded that contains a variable that is passed by reference that is not in a function definition. 

Drupal 7 requires PHP 5.2 or higher and PHP 5 always passes objects into functions by reference

This was a difficult bug to find because enabling a feature of the Date Views module is what triggered it. However, the problem was in the Workbench Moderation module. What I did was set the breakpoint in the debugger on function drupal_set_message() then worked back through the call stack till I found the offending variable.

Problem was not exactly in the Date module but was nonetheless triggered by the Date module in line 53 of date_views_fields.inc.

// If we don't have a filter handler, we don't need to do anything more.
if (!$handler = views_get_handler($table_name, $field_name, 'filter')) {
  continue; 
}


This would iterate through all the view's handlers including workbench_moderatioin_handler_filter_user_can_moderate which passed a variable by reference not in a function definition,     parent::options_form(&amp;$form, &amp;$form_state);. Simply the Workbench moderation module needs to be patched to reflect changes in code in PHP 5.3