Hello all
I appreciate your different advises and propsals. In fact I just found who to deal with the issue. By going throught MD03 you can access directly to thé purchase requisittion and delete directly from there. By saving the MRP proposal, sales order and PR disappear. That's fine.
Anyway I'll keep all the 3 replies, it could help in future.
Thanks to everyone, you're "precious".
Regards
Marc.