QuickForm Validation error when adding event using New Event Wizard

backTrace

/home/drupal/svn/civicrm_v1.7/CRM/Core/Error.php, backtrace, 147
, handle,
/home/drupal/svn/civicrm_v1.7/packages/PEAR.php, call_user_func, 901
/home/drupal/svn/civicrm_v1.7/packages/HTML/QuickForm.php, PEAR_Error, 1988
/home/drupal/svn/civicrm_v1.7/packages/PEAR.php, HTML_QuickForm_Error, 563
/home/drupal/svn/civicrm_v1.7/packages/HTML/QuickForm.php, raiseError, 1531
/home/drupal/svn/civicrm_v1.7/CRM/Core/StateMachine.php, validate, 148
/home/drupal/svn/civicrm_v1.7/CRM/Core/QuickForm/Action/Next.php, perform, 63
/home/drupal/svn/civicrm_v1.7/packages/HTML/QuickForm/Controller.php, perform, 195
/home/drupal/svn/civicrm_v1.7/packages/HTML/QuickForm/Page.php, handle, 95
/home/drupal/svn/civicrm_v1.7/CRM/Core/Controller.php, handle, 213
/home/drupal/svn/civicrm_v1.7/CRM/Event/Page/ManageEvent.php, run, 152
/home/drupal/svn/civicrm_v1.7/CRM/Event/Invoke.php, run, 59
/home/drupal/svn/civicrm_v1.7/CRM/Core/Component.php(171) : eval()'d code, admin, 1
/home/drupal/svn/civicrm_v1.7/CRM/Core/Component.php, eval, 171
/home/drupal/svn/civicrm_v1.7/CRM/Core/Invoke.php, invoke, 603
/home/drupal/svn/civicrm_v1.7/CRM/Core/Invoke.php, admin, 86
/home/drupal/svn/civicrm_v1.7/drupal/civicrm.module, invoke, 288
, civicrm_invoke,
/home/drupal/public_html/drupal/includes/menu.inc, call_user_func_array, 418
/home/drupal/public_html/drupal/index.php, menu_execute_active_handler, 15

New Event Wizard

unrecoverable error
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Error Details:

Array
(
[callback] => Array
(
[0] => CRM_Core_Error
[1] => handle
)

[code] => -1
[message] => QuickForm Error: unknown error
[mode] => 16
[debug_info] => Form rule callback returned invalid value in HTML_QuickForm::validate()
[type] => HTML_QuickForm_Error
[user_info] => Form rule callback returned invalid value in HTML_QuickForm::validate()
[to_string] => [html_quickform_error: message="unknown error" code=-1 mode=callback callback=CRM_Core_Error::handle prefix="QuickForm Error: " info="Form rule callback returned invalid value in HTML_QuickForm::validate()"]
)