MBSA - WUREDIST.CAB is damaged or an invalid Catalog

Configuration (WSUS server in DMZ) (LAN is private with no internet access)
All Servers are 2003 and workstations are XP (at current service pack level)
I run MBSA after each patch cycle from my workstations - (never any issues)
This month I am receiving the following error "WUREDIST.CAB is damaged or an invalid Catalog"
I have replaced files in the cache folder - still no joy!
.. Security update catalog (wsusscn2.cab), available from the Microsoft
Web site
b.. Windows Update Redistribution Catalog (wuredist.cab) located at
http://update.microsoft.com/redist/wuredist.cab
c.. Authorization catalog (muauth.cab) for Windows Update site access,
available from the Microsoft Web site or by examining the contents of the
wuredist.cab file located at http://update.microsoft.com/redist/wuredist.cab
d.. Windows Update Agent standalone installers (if not already installed):
a.. For x86-based computers (WindowsUpdateAgent30-x86.exe) or
b.. For x64-based computers (WindowsUpdateAgent30-x64.exe) or
c.. For ia64-based computers (WindowsUpdateAgent30-ia64.exe), the latest
versions are available by examining the contents of the wuredist.cab file
located at http://update.microsoft.com/redist/wuredist.cab
After downloading the files from the Microsoft Web site, copy all files
listed above to the following folder on the computer performing the security
update scan:
C:\Documents and Settings\<username>\Local Settings\Application
Data\Microsoft\MBSA\2.1\Cache


Anyone have any ideas?

Thanks,
Barb