Vista - Windows defender error message during scan

During a Windows defender scan i get the error message "0x8050800c"

The last successful scan was on 04/02/2009, prior to an new update for
Windows defender definitions.

This message was displayed every time the scan hit a registry entry for VNC.
As I no longer had VNC installed i removed the entry and scan was able to
continue past that point.

However it now fails at the following reg entry;
HKLM\Software\Microsoft\Windows\Currentversion\Internet
Settings\Zonemap\Ranges\Range1\\:range

I am thinking there is some sort of malware that is causing the error. I
have installed Spy bot, Ad-aware, CCleaner run scans with all. And have been
running TrendMicro server security which connects to SBS2003.

Has anyone experienced the same problem?
Can anyone make a recommendation on how to go about fixing this error, or
remove malware/virus?

Now that I have spybot, I am thinking about disabling Defender, but first
want to be sure that my system is not compromised

Assistance is appreciated.

It could be caused by some virus or any protected Software as well.First of all scanning on allive system is not credible because many viruses can hide perfectly before any protected software or even sometines deactivate them.Try this liveCD with antivir Index of /devbuilds/RescueDisk/
burn it,boot it and scan

When you'll finish scan but nothing help try:

1.Try reset IE - try all methods described in this link
Internet Explorer - Reset

2.Disable service Windows Update try manually update definitions for Windows Defender and again enable service Windows Update

3.Uninstall all any non-system protected software