So on a recent reinstall of my Dark Souls: Prepare to Die Edition in Steam I was confronted with a UAC (User Account Control) popup from Windows every single time I started it. Dark Souls used to use Games for Windows Live in the past. As some point it switched over to Steamworks. Unfortunately the installscript.vdf file was not adjusted to reflect this. It still tries to call the gfwlivesetup part of the setup because it never completes and the required registry key is missing. So because of this is falls into an infinite check, popup UAC cycle.

To fix this, open up the registry editor by running regedit, navigate to ComputerHKEY_LOCAL_MACHINESOFTWAREWow6432NodeValveSteamApps211420, in the right pane right-click, select New » DWORD (32-bit) Value and name it gfwlivesetup. Double-click this newly created entry and enter 1 for the value. Exit the registry editor and start Dark Souls. You should not see the UAC popup anymore.

So recently I had an issue with Steam where the Witcher 2 update got stuck at 99% and the status "Update Paused". No matter what I tried with the pause/resume button, I couldn't get it to budge from this status and actually update.

After a while I grabbed Process Explorer from the Microsoft website and checked the files that were being opened when I toggled this state. I noticed a reference to Steamsteamappsdownloading20920CookedPCpack0.dzip. Then I also noticed a file reference to Steamsteamapplogscontent.log. Upon checking that file I found a notice that it was trying to preallocate about 11 GB for this pack0.dzip. Checking my drive status, I saw that this particular drive letter only had about 9 GB left. Freeing up some space allowed the update process to actually start and finish, after which I got even more space back, since it seems Steam downloads these files and then replaces them, deleting the temporary one. So I guess the lesson learnt is that you should always have enough disk space free as the single largest file in any of your games.