mrkitano: It happened to me too. I noticed that in the witcher site forums people who complained about it had one or two parts from the predownloaded patch corrupted. The have since fixed it, but maybe the gog version still has the same two parts broken.
I actually had a corrupted Core0 package and I found online that in order to install my Enhanced Edition I had to download from the witcher site Part 1 and 2 of the patch for it to work.I did it like that and I could install it and yet the problem persists.
I really hope someone has an fix for that,I really want to see the extra content this patch provides(especially the cutscenes).