problem for upgrading plesk

[websat]

Hi
i can't upgrading my plesk 8.0.1 i have the errors:

Avertissement: Erreur : failed to open lock file /tmp/psa-installer.lock: Permission denied.

Erreur: Impossible de déterminer le statut de l'installation : failed to open lock file /tmp/psa-installer.lock: Permission denied

If someone can help me... thanks