Sorry for the late answer.
Thank you for your replies.
I search further more in the scn, and I found a nice Wiki about this topic.
http://wiki.sdn.sap.com/wiki/display/BOBJ/SAP+ECC+Systems+SP+Upgrade+and+Impact+on+SAP+BI
This link help me a lot with the check list of actvivities to do when an upgrade is perform in the ERP source system of BW.
Thank you.