SBS 2011, like SBS 2008, is designed to fully support IPv6 and has IPv6 enabled by default.  Most users should never need to disable IPv6, however if you must disable IPv6 here is how to disable it properly:

Important: This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base: 322756 (http://support.microsoft.com/kb/322756/)

1. Uncheck Internet Protocol Version 6 (TCP/IPv6) on your Network Card.
2. In Registry Editor, locate and then click the following registry subkey: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip6\Parameters\
3. Double-click DisabledComponents to modify the DisabledComponents entry.
   Note If the DisabledComponents entry is unavailable, you must create it. To do this, follow these steps.
   • In the Edit menu, point to New, and then click DWORD (32-bit) Value.
   • Type DisabledComponents, and then press ENTER.
   • Double-click DisabledComponents.
   • Enter "ffffffff" (eight f’s), and then click OK:
   • Reboot the SBS 2011 server. RRAS (VPN) Note: If you plan to enable VPN on your SBS 2011 server, you MUST also Export and then Delete the following registry key: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\RemoteAccess\RouterManagers\Ipv6

If you do not delete this key you will get an 20103 Event when trying to start RRAS with IPv6 disabled.  You must reboot after removing this key.