Please post a screenshot of when this error message appears, at your earliest convenience.

That is a VERY interesting problem (sorry, being a QA guy, all problems are interesting, but I guess it's irritating to you guys).

It would be great if you could contact support directly with as many information and reproduction steps as you can. Firek can redirect you to us and we can contact you directly to help solve this problem.

1) What OS and what version of it you have installed
2) What is the path you are trying to install in
3) Are other GOG installers working for you?
4) What are the exact steps you performed?
5) Are there any background processes running, like skype, antivirus, firewalls, games, other installers etc.
6) DxDiag.

These are just some off the top of my head.

I have a more specific question - how soon does it happen after the progress bar appears? Is it immediate, or does it take a couple of seconds?
Does it happen in any other installer from GOG?

Could you post a screenshot of your list of processes in Task Manager when the error appears? You can send it via PM to me if you don't want to post it here.

Thank you both for the screenshots.

@ChrisMes: I don't see the installer process at all in your screenshot (should be "setup_the_witcher_adventure_game..."). Could you make another screenshot and click the "Mostrar procesos de todos los usuarios" at the bottom left? I'd like to check which processes the installer has started, so I can pinpoint the moment it crashes.

Also - if the error appears when you right-click the window or move it, then what happens if you just wait? Is the installer just frozen at the beginning of the installation until you click it? Do the images in the background change after some time?

Please make sure that you have downloaded the latest version of the installer, and try launching it with this parameter:
/force_launcher

To do this, you should either launch the installer from the command prompt, or create a shortcut for the installer, and edit it to contain this parameter.

Please let us know if this helped.