When I try to launch Prism 3 using OLE automation, Windows tries to launch Prism 4 (which I no longer use).

You can launch Prism from another program using the OLE automation command:
     Set pz=CreateObject (' prism. command')

This same command launches Prism 3 or Prism 4. When you run Prism 4 (regular or demo), it resets the Windows registry so that OLE automation command launches Prism 4 rather than 3. That's great... until  you uninstall Prism 4. Now OLE automation tries to launch Prism 4, which no longer exists on your computer.

To fix this problem:

1. Quit Prism
2. Download and launch this registry file. It will fix the registry, so the OLE automation will launch Prism 3, not 4.
3. Launch Prism 3, then quit
4. Run your OLE automation script, which will now launch Prism 3 rather than 4.

You should only have to run this once, at least until the next time you run Prism 4 on that computer.