I got this checksum error 3 with the old gog downloader i have installed galaxy as it adviced but i have to DOWNLOAD itagain?!There is no option just download again while i already have the files what the hell is this?i have slow internet i took me 2 goddam days to get this game i now i have to download again because of this crappy downloader fucked up the install files?
This is a fuckin bs its not working what ever i try to do its just starts download the whole game again thank you GoG for this bullsdhit even ppl who pirating the game thay able to play while i have the original one and can do nothing just wait MAYBE if i download again for 2 days at least MAYBE its gonna work.

EDIT: i restarted the old downloader and its downloading the reamaining 2 gb, which is strange because earlier its showed complete but seems like it wasn't.Sorry if i went a bit crazy about this but u ppl can understand the dissapointment after days of waiting.Hopefully its gonna work now.Peace!

I ahve the same problem, but with die CD-Version. I bought them, wanted to install them and at the first CD the error appears: Checksum Error -3.

I restarted the installationen for many times, failed every time
I tried to install it on another HDD, failed
I copied the files on my HDD, failed

I installed it on another system - it works. But how do i find out what chrashes my installation ?

Strange.It shoud work on the firts system too, i have no idea what cause your problem maybe the op system was different on the first try? Meantime i think i found my solution i hope.The file wasn't completly downloaded for me despite the client showed the progress is done.It's downloads now the missing 2 gb if it's gonna work i will update this post.

I will try two more things:

For the case that the files on the retail CDs are damaged, i download them again.
Also I'll try the CDs from a friend.

I let you know if that helped me.

I was able to install the game after downloading the missing part.:)I had similar problem with GTA V the disc was scratched.I asked for a replacement but the replacement disc was damaged too.I was able to mix and match a working copy from the two boxes.If you have high speed broadband try to use your key here or on the steam and download it.

Here's the solution:

Copy the games folder of a working installation from a friend and paste it on your harddrive.

Start the witcher.exe and have fun.

same problem, and iam helpless