Anyway - the symptoms are that after you plug in the camera, Windows recognizes it, but the download window doesn’t show up. For one user, it works, for the other it doesn’t. The weird thing is that I could watch the process list and see the app (CameraWindow.exe) start, but then quit without showing any error message.
After much mucking about, I tracked it down to the permissions on the registry keys. One user had permission to modify the keys, the other didn’t, so the application quietly failed. I couldn’t even re-install the app, as I didn’t have permissions to write to the HKLM\Software\Canon key.
To fix it, I uninstalled as much as I could, switched users to find who had permission to alter the registry key, deleted it, then reinstalled the software. I actually reinstalled (the same version) for all users this time, but probably could have just modified the permissions on the registry keys for all users to have access.