Geromino: Yep they rolled the first Hotfix 4 back and thus dont offer a way to undo the fix. Therefore once you have the bad Hotfix, a complete reinstall is the only option.
melandis1973: Assuming you've saved your offline installers, you don't need to redownload the latest version of the entire game.
You can reinstall using those original files and patch installers - once you're at hotfix 3 just install the new hotfix 4 installer.
Since I dont use it, I dont know anything about the GoG installer client. If theres an option for that, great. My impression was that you just run this thing and dont get any saves for the downloads that thing does.
Which means if you have a new machine you have to download everything again.
In my case I enjoy very much having the games I own actually as a finished product in hand, able to install them on any new machine again without download should both my old computers and the internet break down.