exception 'Doctrine_Validator_Exception' with message 'Validation failed in class Image

  1 field had validation error:

    * 1 validator failed on user_id (notnull)
' in /home/admin/domains/pixhub.eu/public_html/lib/doctrine/Doctrine/Transaction.php:265
Stack trace:
#0 /home/admin/domains/pixhub.eu/public_html/lib/doctrine/Doctrine/Connection.php(1395): Doctrine_Transaction->commit(NULL)
#1 /home/admin/domains/pixhub.eu/public_html/lib/doctrine/Doctrine/Connection/UnitOfWork.php(148): Doctrine_Connection->commit()
#2 /home/admin/domains/pixhub.eu/public_html/lib/doctrine/Doctrine/Record.php(1718): Doctrine_Connection_UnitOfWork->saveGraph(Object(Image))
#3 /home/admin/domains/pixhub.eu/public_html/controller/images.php(169): Doctrine_Record->save()
#4 /home/admin/domains/pixhub.eu/public_html/controller/frontController.php(54): ImagesController->showAction()
#5 /home/admin/domains/pixhub.eu/public_html/init.php(37): frontController->init()
#6 /home/admin/domains/pixhub.eu/public_html/index.php(11): require_once('/home/admin/dom...')
#7 {main}