Microsoft SQL Update Error

Can anyone help?
We are using SBS 2003 Standard Edition without the new SP1
An overnight update is failing (every night). The event log lists two
errors:-
Error 1023
Product: Microsoft SQL Server Desktop Engine - Update
'{1F506503-186B-4D88-81B3-7113B9457C9D}' could not be installed. Error code
1603. Additional information is available in the log file C:\WMSDEHotfix.log.

Error 10005
Product: Microsoft SQL Server Desktop Engine -- Internal Error 2727.
DatabaseRepl.185C1D8F_1545_4277_BB64_857D2622DB57

The last lines of a very large WMSDEHotfix log show:-

Property(S): DATABASE = C:\WINDOWS\Installer\22fc40.msi
Property(S): SqlStartType = 2
Property(S): PATCHNEWPACKAGECODE = {505DF605-4FA3-45BC-B054-0DEC2EAF9234}
Property(S): PATCHNEWSUMMARYSUBJECT = SQL Server 2000 Desktop Edition
Property(S): ProductState = 5
Property(S): SOURCEPROP2 =
C:\DOCUME~1\ADMINI~1\LOCALS~1\Temp\IXP000.TMP\sqlr un16.msp
MSI (s) (F4:90) [09:36:52:312]: Product: Microsoft SQL Server Desktop Engine
- Update '{1F506503-186B-4D88-81B3-7113B9457C9D}' could not be installed.
Error code 1603. Additional information is available in the log file
C:\WMSDEHotfix.log.

MSI (s) (F4:90) [09:36:52:312]: Attempting to delete file
C:\WINDOWS\Installer\15d4e2e.msp
MSI (s) (F4:90) [09:36:52:328]: Cleaning up uninstalled install packages, if
any exist

Any ideas?
Thanks
Peter Smith