The error message you are seeing is pretty clear - you haven't provided credentials that it can correctly authenticate with.
You say you are connecting to a server - so what account are you expecting to use to authenticate against the server? A domain account, or a local account on the server?
The arguments you are providing are
Serv_UName, "",Serv_Pwd
What is the middle argument? Is it 'domain'? If so, try the following
Serv_UName, Serv_Name, Serv_Pwd
So if I wanted to connect to a server called SERVER1 with account dmorley, it would read
using (new Tools.Impersonator("dmorley", "SERVER1", "S0mePa55word"))
You need to make sure that the account exists on the server you are connecting to