Thx for your answer and your post !

Actually, I think this is an OS issue, maybe explained here : http://serverfault.com/questions/451387/how-to-delete-cached-temporaril…

Since the problem occurs on a PRD quite big Production, I have to be careful.

But I found a workaround : instead of using the host name, I just replace with the IP address and it works fine.

\\srv-appname\mypath\

is just replaced by

\\192.168.0.16\mypath\

Thx, now I understand why the  OSUserName() function returns " _Ensemble". Sorry, I didn't read this documentation before posting.