If you are unable to load HTTP web pages however secure (HTTPS) webpages load fine then you need to ensure this registry entry is in place. This should be part of your initial setup process for SBS 2011.
- Start Registry Editor (Regedit.exe).
- Locate the following registry key:
- On the Edit menu, click New, click DWORD (32-bit) Value , and then add the following value:
Data Type: DWORD
Data value: 0x2A300 (172800 in decimal = 2 days)
- Click OK .
- Quit Registry Editor.
- Restart the DNS Server service.
This key determines how long the DNS server can save a record of a recursive name query.
More info here.