Exchange Server 2003 - Can't connect to exchange server in same machine

I have an Exchange Server running in a remote machine.
We also have an application that connects to this Exchange Server through ActiveDirectory and Independentsoft's WebDav.
This works perfectly when I run the application locally, but if I install it in the machine where the Exchange Server is running I only have connectivity with Active Directory, through WebDav I can't access any mailbox with the following URL template "LDAP://MyDomain/exchange/test@test.com", the Exist() method returns false.

Using this code:

"
var _Credential = new NetworkCredential(domain.AccessUsername, domain.AccessPassword);
var _WebdavSession = new WebdavSession(_Credential);
_WebdavSession.UserMailbox = _Url;
var _Resource = new Resource(_WebdavSession);
_Resource.Exists(); <-------
"



In the other hand, I installed the application in another machine and tried to do the exact same but I couldn't connect by ActiveDirectory, I get a "The server is not operational" (0x8007203A) error; through WebDav I get "System.Net.WebException: Unable to connect to the remote server ---> System.Net.Sockets.SocketException: A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond".

All this with exactly the same LDAP URL, credentials, and everything.

Any help would be appreciated.

In the end I solved it, it seems to be a problem with Amazon servers: you can't connect from one to another, but you CAN connect to 127.0.0.1 (but not, for some reason, to localhost).