Link : [1] http://support.microsoft.com/kb/948496

Reasons to turn of SNP:

- When you try to connect to the server by using a VPN connection,
you receive the following error message:
Error 800: Unable to establish connection
- You cannot create a Remote Desktop Protocol (RDP) connection to the server.
- You cannot connect to shares on the server from a computer on the local area network.
- You cannot join a client computer to the domain.
- You cannot connect to the Exchange server from a computer that is
running Microsoft Outlook.
- Inactive Outlook connections to the Exchange server may not be cleaned up.
- You experience slow network performance.
- You may experience slow network performance when you communicate
with a Windows Vista-based computer.
- You cannot create an outgoing FTP connection from the server.
- The Dynamic Host Configuration Protocol (DHCP) server service crashes.
- You experience slow performance when you log on to the domain.
- Network Address Translation (NAT) clients that are located behind
Windows Small Business Server 2003 or Internet Security and Acceleration (ISA)
Server experience intermittent connection failures.
- You experience intermittent RPC communications failures.
- The server stops responding.
- The server runs low on nonpaged pool memory

Solution:

Method 1: Manually disable Receive Side Scaling and TCP Offload in the network adapter driver

To manually disable RSS and TCP Offload in the network adapter driver, follow these steps:
1. Click Start, click Run, type ncpa.cpl, and then click OK.
2. Right-click a network adapter object, and then click Properties.
3. Click Configure, and then click the Advanced tab.
4. In the Property list, click Receive Side Scaling, click Disable in the Value list, and then click OK.
5. In the Property list, click TCP/IP Offload, click Disable in the Value list, and then click OK.
6. Repeat steps 2 through 5 for each network adapter object.

Method 2: Update the network adapter drivers

To determine whether an updated network adapter driver is available, contact the network adapter manufacturer or the original equipment manager (OEM) for the computer. The driver must meet Network Driver Interface Specification (NDIS) 5.2 or a later version of this specification.

Method 3: Manually disable RSS and TCP Offload in the registry

To manually disable RSS and TCP Offload yourself, follow these steps:
1. Click Start, click Run, type regedit, and then click OK.
2. Locate the following registry subkey:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters
3. Right-click EnableTCPChimney, and then click Modify.
4. In the Value data box, type 0, and then click OK.
5. Right-click EnableRSS, and then click Modify.
6. In the Value data box, type 0, and then click OK.
7. Right-click EnableTCPA, and then click Modify.
8. In the Value data box, type 0, and then click OK.
9. Exit Registry Editor, and then restart the computer.