So I've been struggling with installing Witcher 3 on my PC for the past two days. When trying to install (or update with today's 1.03 patch) in Galaxy, it always fails. The error I'm given says: "Installation failed: out of disk space". I have an SSD and a HDD, and I've installed both Galaxy and W3 on my HDD, which has over 300GB of available space. My SSD also has 100GB+ available space. So I don't really understand why this is happening. I had none of these issues with my second computer.

So, anyone experiencing similar issues? I can't think of any reasons why this doesn't work.

Many folks are having a range of issues. Try downloading the patch using the website under your account and leave Galaxy alone for a little while until that get Galaxy behaving with W3.

Galaxy has so many issues (since it's beta) that I think it's best if you use the webpage to download upgrades. I didn't had problem with that... You ninja you :)

If the above suggestions don't work, there was another thread in the last day or two talking about the same problem. Here is one of them:

http://www.gog.com/forum/the_witcher_3_wild_hunt/installation_failed_out_of_disk_space

Note that it's found in the subforum for TW3, so you might want to post future questions over there for game-specific responses.

Make sure you have read and write permissions not just for the game folder, but also your GOG download folders (whatever you have them set to).

https://technet.microsoft.com/en-us/library/cc754344.aspx

So this is what worked for me. First, I needed to uninstall GoG. Then I would install GoG to the same drive I wanted to install my games, E.G. I wanted my games on F: so I install the client to F: as well (this as apposed to client installed on C: drive and games to F: drive) Once I did that I had to go into the setting and make sure the games were set to manually control and make sure the games installed to the same drive as the client and there was enough room. If I tried to install even once to a drive that didn't have enough space the error would not go away and no matter what I did the game would not install. So in summary

A) Install client to a drive that has enough space and the same drive as the one you want your games on
B) Manually control where the install goes
C) Make sure you have the proper drive selected before you try to install the game or it will mess up and make you uninstall and reinstall the client.

I hope this helps people.

The "Manually control where the install goes" solution didn't work for me.

Here's what did:
-Make sure you're running GOG Galaxy as administrator (doesn't hurt)
-Go to the install folder (the path will be in the GOG Galaxy settings under Folder > Install Game)
-Right-click that folder and go to Properties > Security
-Edit permissions and give Full Control to your user. I gave full control to "ALL APPLICATION PACKAGES" as well but you may not need to
-Try to install