Invalid instance error when installing MSDE service pack 4

This one came up during a software upgrade for Sophos Enterprise manager. It turns out that the upgrade need was in fact three different updates – but that none could take place without the version of MSDE being at SP4. I checked and found mine had no service packs applied. So after downloading and unpacking the update tried to run it and got a message “Invalid instance name”. After trying all the variations of the instance names which I knew to be SOPHOS found that the following string allowed the update to run successfully

setup.exe /upgrade sqlrun blanksapwd=l /L*v “c:msde4.txt”

The issues here were – if run without any parameters the setup refused to run until the sa account had a hardened password set but this was not correct since the database instance was in Windows authentication mode not SQL. The instance name is not specified and on checking the log file c:msde4.txt I can see that the instance was successfully updated to SP4 with

Windows Installer reconfigured the product. Product Name: Microsoft SQL Server Desktop Engine. Product Version: 8.00.2039. Product Language: 1033. Reconfiguration success or error status: 0.

As a note – I used osql -U sa  and osql -E to confirm that the authentication was not SQL. In the first instance the logon will fail if you try the default blank password since its not configured for this – the -E will allow you to logon and get to the osql prompt to issue commands.

The upgrade to Sophos Enterprise Manager completed without incident to v 4.02 after this and will be updated to 4.5 once the configuration is updated for the the new sophos update manager.