errore fetch_assoc()

[Trommo]

Error: Call to a member function fetch_assoc() on a non-object

function getProjectValues($project_code){   


    $conn = new mysqli("localhost","root","password","prova") or die("Error " . mysqli_error($this->MSQLI_CONNECTION));     $result = $conn->query("SELECT project.project_Name, project.project_Password, project.project_Folder FROM project INNER JOIN user ON project.project_Code = $project_code ");     

    while ($row=$result->fetch_assoc()) {                                         echo $row['project_Name'];                 echo $row['project_Password'];                     }         } 

Sapete darmi una soluzione? grazie in anticipo.