Thanks a lot for your help.
I think the file was realy corrupted because there was a message at the opening saying that it was corrupted: in Excel5 => Message => possible to open file but there was some hieroglyphes inside. in Execel 2007 => message => and impossible to
But i have found the solution : it was the : requireonce() function (including the conection login script) who made this problem. And i 've try whith include(), includeonce(), require() and it's the same
So i simply put the 4 lines naking connection directly in my phpexcel script and every thing is right.
If you have any questions, or if you want a sample of the generated file ...
Sorry about my bad english,