The error Setup cannot continue because setup programs are missing is because setup.exe on your server is version 6.1, but the other setup files on your server are version 6.0 (the setup version is independent to the QuickMap version).

One way this could happen is if the QuickMap upgrade Disk 2 is manually copied onto the server.

Normally the monthly update is applied by running setup.exe from Disk 2. If the latest update disk has been installed by manually copying the disk, the install will need to be done again but this time by running setup off the CD-ROM.