>>>As I just described to Hank, the application EXE and the set EXE are two different programs. So, if any ActiveX components got wiped out or whatever, the main application EXE would show an error. The main EXE knows nothing about the SETUP.EXE
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>>Are you sure? If the setup was generated in anyting using m$'s tools (forgot the name, just that it uses .msi extension), then it wrote in the registry which setup installed the app, so yup, the app itself wouldn't know, but Windowses would. Happened exactly the same way each time we had that. And mind you, our setup was generated in Inno, except the runtimes setup, which was a .msi - and then it went that way.
>
>What you write may make sense. The SETUP.EXE used to be created using InstallShield, a MS product. Some years later I changed the SETUP.EXE to use InnoSetup. But it could be that the "old" setup is still in the Registry of the PC. What puzzles me is that it seem to have happened with - at least - two different desktops.
>But I will check the users' drives for a MSI programs and delete them, if they exist.
>Thank you.

In this case, the customer should see two entries in the apps list. The customer should remove both (I have no idea what order is best) and reinstall the recent. Else it is not sure what files will survive.

InstallShield was never a MS product, we only had one IS-Express with a VFP Version. But InstallShield is using the msi / msiexec system.
MS hands a SDK to deal with MSI files, but this is as odd as it comes. In the days of yore I've used it to fix some stuff, but I own a copy of InstallShield, so I use this to fiddle with the msi I have to crack.