SandBox Problem with HardDisk

Hello !

First , Sorry if my english isn't totally clean.

Here is my problem, i hope you can tell me some tips :) :

I'm trying to config Steam in an isolation environement to launch it twice : This is for playing with my wife with just one computer (but i'm using Aster to make Two WorkStations).

The probleme is , when i try to config it on full access (SandBox Settings -> File Access -> Full Access -> add) It just Shows my user file (i took a screenshot^^).

 

But.. obviously, my steam location is located to my "C:" HardDisk. Am I Mistakening something in the process ?

i also tried to copy my steam file to my user location, a weird idea... I was able connect to steam Twice, but can't access to my friendlist,neither launching a game. so i think this isn't the deal..

If someone can unlock my situation, it will be really nice :) please :)