That is not a solution!
in file application/models/projects/Project.class.php on line 451 in SQL condition the ? sign is missing:
$wsBilling = WorkspaceBillings::findOne(
array('conditions' => array(
'project_id = ? AND billing_id = ',
$this->getId(),
$billing_category_id
))
);
And should be like that:
$wsBilling = WorkspaceBillings::findOne(
array('conditions' => array(
'project_id = ? AND billing_id = ?',
$this->getId(),
$billing_category_id
))
);