Nuran_659@Pack!? の投稿を引用：

- Unable to find gameinfo.txt. -

Right-click Source Filmmaker in your Steam library, and choose "Manage" > "Browse local files".
A File Explorer window should now pop up in -/steamapps/common/SourceFilmmaker/. In this window, hold Shift while right-clicking the "game" folder, and choose "Copy as path".
Then press the Windows key, search for and click on "Edit the system environment variables", and click "Environment Variables...".
Now click on the "New..." button in the upper half of the window that just popped up, type "VGame" (without quotes) as the variable name, and paste the path to the "game" folder that you copied earlier as the variable value. Click "OK".
After that, click on the "New..." button in the upper half of the window again, type "VMod" (without quotes) as the variable name and "usermod" (without quotes) as the variable value, click "OK" again, click "OK" once more, and click "OK" a last time.
Lastly, reboot your computer, to make sure that the changes take effect, and then check whether Source Filmmaker works now.

(You don't have to delete the old "VGame" and "VMod" variables first; creating new variables with these names will replace the existing ones.)




If that doesn't fix it, then right-click Source Filmmaker in your Steam library again, choose "Launch" to open a pop-up selection menu, select "Launch SDK" in it, click "Launch" to open the SDK, make sure that the drop-down "mod" selection list is set to "usermod", click "Reset Game Configurations", follow and agree to the prompts, reboot your computer, and check whether it works now.




If that doesn't fix it either, then right-click Source Filmmaker in your Steam library again, choose "Properties..." > "Local Files" > "Verify integrity of game files...", wait for it to finish, and allow Steam to re-download anything that it wants to for Source Filmmaker now, then check again after that's done.

Hello Mr. Zappy, thank you so much for helping me solve the error.
Everything works fine for me now!