How To Use TCP/IP To Connect Remote SQL Server In A .asp ?

I have 2 Window 2000 servers. A server is a Web server (IIS 5.0). B server is a MS SQL 2000 database server.

I use the following connection string to connect successfully the B DB server from the A server.
....
cnstr = "Provider=SQLOLEDB;Persist Security Info=False;UID=xxxx;PWD=xxxx;Data Source=xxx.xxx.xxx.xxx;Initial Catalog=DDDDD;"
Set conn = Server.CreateObject("ADODB.Connection")
conn.Open cnstr
......

But, I change the connection string to the following (it just only be added "Network=DBMSSOCN;", it is connecting with TCP/IP). It is failed !
....
cnstr = "Provider=SQLOLEDB;Persist Security Info=False;UID=xxxx;PWD=xxxx;Data Source=xxx.xxx.xxx.xxx;Initial Catalog=DDDDD;Network=DBMSSOCN;"
Set conn = Server.CreateObject("ADODB.Connection")
conn.Open cnstr
......

The error message is :
Microsoft OLE DB Provider for SQL Server error '80004005'
[DBNETLIB][ConnectionOpen (Connect()).] General network error.Check your network document
/TCPIP_Test.asp, line 14


Then, I use the same connection string (TCP/IP) to connect successfully the B DB server from an other C web server.

Other test on the A server :
1. ping -a <B server> : test OK !
2. telnet <B server> 1433 : test OK !
3. osql -U<xxxx> -S<B server> : test OK !
4. run VB6 apps with the TCP connection string : test OK !

What is problem in my A web server ?