As John pointed out a few minutes ago, you can manually update Defender on
32-bit machines:

1. Go to http://www.microsoft.com/security/portal/ADL.aspx

2. Click on the link on the left side of the page to download/install the
new update. Do not use the link in the right-hand menu under "Latest
Definition Updates".

The linked download appears to be a re-release of definitions v1.35.563.0
which were originally released on 19 Jun-08. Installing it will make
Defender "happy" again. <wink>
--
~PA Bear


PA Bear [MS MVP] wrote:
> Update on the situation: MS apparently "recalled" the Defender update
> released on 24 Jun-08. If the Defender "Alert!" icon is still displaying
> in
> Notification Area, open Defender and click on Check for Updates. You
> should
> get a "No updates available" response and Defender should be happy again
> (at
> least if you didn't uninstall/reinstall Defender).
>
> PA Bear [MS MVP] wrote:
>> [Crossposted to Windows Update, WinXP General, and Security newsgroups]
>>
>> I have reproduced this problem (error 0x80070643). Users may encounter
>> this
>> problem when updating Defender via Automatic Update, Windows Update, or
>> from
>> within Defender (Check for updates function).
>>
>> NB: Defender will NOT be happy and its "Alert!" icon will continue to
>> appear
>> in Notification Area until an update is successfully installed. This
>> does
>> NOT mean that Defender is not working/protecting your machine.
>>
>> I have alerted MS and the Defender team to this apparent bug via private
>> channels.
>>
>> Serge wrote:
>>> Automatic update set to: Notify me but don't automatically download and
>>> install them. It downloads ok.
>>>
>>> It failed to installed no error code.
>>>
>>> I tried to download it manually.
>>>
>>> The window showed:
>>>
>>> Initializing Installation
>>> Download
>>> Not Installed
>>>
>>> As it keeps being reoffered, I now have it as a hidden update.
>>>
>>> Serge