Hello Jeanselme,
Based on the available power you shared (7989) your enclosure has sufficient resources to power on the server. Normally such messages incur when there is a miscommunication between OA and iLO. Based on your OnBoard Administrator (OA) firmware version which is dated (~2012) iLO should be around the same level/date (or slightly newer). Subsequently a starting troubleshooting point would be OA & iLO firmware versions. Most notable, if enclosure interconnects are Virtual Connect modules, prior any upgrades consult the interoperability matrix https://support.hpe.com/hpsc/doc/public/display?docId=mmr_kc-0100204