OK
Thank you Matt for the reply...it will make me relax during the week-end , otherwise I was going crazy !
I could have a coordinate ( WGS1984UTM zone 54N) . but it induced a lot of other problems in other instances,so one day I decided to go to "no projection option" and it made my life easier for my project. This is life ,you have to make a choice !!
Cheers,
Flore