If PostgreSQL cannot be installed, this might be because the Windows service for secondary users (“Secondary Logon”) is not running.
Make sure that this service is currently running and launched at system startup. To do so look it up in the Windows Services. You can get to the Windows Services by opening the control panel, double clicking “Administrative Tools” and opening “Services”. Search for the service with the name “Secondary Logon” (German: “Sekundäre Anmeldung” / French: “Ouverture de session secondaire”) and see if its status is “Started” and its startup type is “Automatic”.
If the service is not started, right click on it and choose “Start” to launch it.
If the service is not launched at startup double click on it and set the startup type in the opening window to “Automatic”.
If there are still problems while installing PostgreSQL, try to install PostgreSQL manually, as the silent launcher, which is used for the GECAMed installation, doesn't show a detailed error message if something goes wrong, whereas the default installer does.