WOWfreegames: Ok, I'm confused. I went into the directory( which for me is C/Program Files(x86)/GOG GALAXY) and looked into the plugins folder, and there is no subfolder for steam. There is one for EPIC and one for Xbox, but no steam. So I just made one, named it the same as the other two and put the new files in there. Nothing. What am I doing wrong? I reinstalled GOG GALAXY twice now. Anyone?
piratul: You got the folder wrong. It's located in %localappdata%\GOG.com\galaxy\plugins\installed\
Be sure to reinstall GOG as you could have broken a few things messing in the wrong folder. Try to connect to steam with the broken default steam plugin just so that it downloads and installs the broken steam plugin.
Exit GOG client.
Just hit WINkey+s and type %localappdata% in the windows search box. It should take you directly to the appdata\local folder. From there navigate to the gog.com folder and all the folders mentioned above. Search for the steam folder in the installed directory. It should look like steam_bunch of numbers and letters. Delete all the contents from that steam folder and copy the fixed version there. Start GOG galaxy and it should work now.