Error in Volunteer Module

Hi

I am getting this error when a a user tries to fill out the volunteer form for an event:

error

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

[code] => -3
[message] => DB Error: constraint violation
[mode] => 16
[debug_info] => INSERT INTO civicrm_group_contact (contact_id , status ) VALUES ( 1 , 'Added' ) [nativecode=1216 ** Cannot add or update a child row: a foreign key constraint fails]
[type] => db_error
[user_info] => INSERT INTO civicrm_group_contact (contact_id , status ) VALUES ( 1 , 'Added' ) [nativecode=1216 ** Cannot add or update a child row: a foreign key constraint fails]
[to_string] => [db_error: message="DB Error: constraint violation" code=-3 mode=callback callback=CRM_Core_Error::handle prefix="" info="INSERT INTO civicrm_group_contact (contact_id , status ) VALUES ( 1 , 'Added' ) [nativecode=1216 ** Cannot add or update a child row: a foreign key constraint fails]"]
)