I have finally found a solution to resolve my problem. 
I was desperate to have tried manymanipulations that doesn’t solve my problem so I decide to run a full maintenance on my computer disk.
Before that I have uninstalled eLCC and cubase.
So I use a software like coktail it’s call “Onyx” in french that can launch all those maintenance scripts :
- repair the disk permissions
- Run periodic maintenance scripts( daily weekly and monthly )
- cache cleaning (system, user…)
And after restarting I have reinitialized the computer PRAM (restart 3 times with cmd+alt+P+R)
Then I have re-installed eLCC 6.3 and Cubase LE5… and… yeah it works !
I have run the same maintenance on another computer with MacOsX10.6 installed on which eLCC doesn’t run and after it was working too.
Sorry for the mistake : it wasn’t an incompatibility between eLCC an MacOsX10.6 it was just probably a permission problem or something like this.
thanks again for the help