If IE6: See
http://support.microsoft.com/kb/946627 (KB946627 is offered as
an Optional/Recommended update via Automatic Updates and at Windows Update
website).
If IE7:
Error message after you install a Windows Internet Explorer 7 update from
Windows Update or from Microsoft Update: "Webpage cannot be displayed":
http://support.microsoft.com/kb/942818
If tweaking your third-party firewall's settings don't help, try the
following:
1. Disable your anti-virus application, any real-time protection provided by
an anti-spyware application (except for Windows Defender; includes Spybot
Tea Timer, SpySweeper Guards, AVG AS guard.exe, etc.), disable any
third-party firewall AND enable the Windows Firewall.
NB: You're "working without a net" now: Don't to ANYTHING else online (e.g.,
browsing; reading email; chatting) except #4 below until your anti-virus
application has been re-enabled! If you're running ZA Free firewall, you
may need to uninstall it instead of disabling it.
2. Uninstall "Security Update for Windows Internet Explorer 7 (KB942615)"
via Add/Remove Programs (make sure Show Updates box is checked at top right)
and reboot.
3. Re-do #1 above.
4. Go to
http://windowsupdate.microsoft.com and install any Critical Updates
offered. If "Root Certificates" update is listed in the Optional Updates
category, you might install it, too, to take full advantage of IE7's
additional security.
5. Reboot > Make sure everything in #1 above is enabled again and, if
applicable, disable the Windows Firewall and enable your third-party
firewall.