KB2596911 is a security update for Sharepoint 3.0. After installing it, you might find that you cannot access Companyweb.
Don’t fear … there are several different suggestions that you may need to try to resolve this issue:
First, try rebooting your server, even if KB2596911 does not require a reboot.
If that doesn’t fix the problem, then try running the Sharepoint Products and Technologies Wizard (Start –> Administrative Tools). If that completes successfully, recheck Companyweb – and hopefully it works! If so, you’re all done.
If that doesn’t fix your problem, then check out this blog from the SBS team that addresses some additional steps when encountering issues with updating Sharepoint on SBS: