Please check out the excellent advice in the other reply--that's the
troubleshooting steps recommended by Microsoft.
In addition, the developers are interested in direct feedback about this
issue. Specifically, they'd like to see the "errors.log" file from machines
experiencing this problem,
This file is located in the installation folder for Microsoft Antispyware,
typically c:\program files\microsoft antispyware.
If you can send this file to:
(e-mail address removed)
with details in the email message about the error message and circumstances,
that'd be helpful to the beta process.
Thanks!