I came across an issue on SBS 2003 and SBS 2008 accessing http://companyweb on the server, after installing the cumulative security update for Internet Explorer (963027 or 969897) or Internet Explorer 8.0 or Windows Server 2008 Service Pack 2.
To fix the problem
SBS2003
On an SBS 2003 server this issue can be fixed by applying update KB961143.
Note: You must have .NET Framework 2.0 installed before you apply this update.
SBS2008
On an SBS 2008 server this issue can be fixed by applying SBS 2008 Update Rollup 2 (960911). This update is now available on Microsoft Update and WSUS.
Or you can use this method KB963027