Exchange connection 401 unauthorized

here the situation :

i'm a interns on an it departement in a big firm and i have to write a little program to calculate the size of an exchange mailbox.

here the code:
Dim client As IEWSClient = EWSClient.GetEWSClient("https://myserverexchange/ews/exchange.asmx", "login", "password", "domain")
this line throw an exception : 401 unauthorized

a little precision :
this line work fine at home but not when i am inside the company.

the company has an intranet and a proxy

the thing i wan't to know is :

does my code have a problem in it ?

or does the exchange server simply refuse my request because of a bad configuration ?

thanks for your help and sorry for my bad english (it's the first time i'm posting a message on a forum)