cakephp SQL error at $this->User->saveField()

[bobcat]

When I try to update a user, let's say his account balance\[code\]$this->User->id = $validUserId;$this->User->saveField('balance', 100);\[/code\]I get this error\[code\]SQL Error: 1054: Unknown column 'User.group_id' in 'field list'\[/code\]with this automatically generated query druring the save process\[code\]SELECT `User`.`group_id` FROM `users` AS `User` WHERE `User`.`id` = *validUserId* LIMIT 1\[/code\]The user belongsTo a UserGroup and therefore the user has user_group_id attribute, is there any way to tell cake, that the attribute is related to a UserGroup?Thanks in advance,EL