Failed to load Launcher DLL error
From Valve Developer Community
After the map compile process has finished, the following error might occur:
Failed to load the launcher DLL: The specified module could not be found.
Update the game files
First and foremost run the game (Half-Life 2, Counter-Strike: Source, Team Fortress 2, etc.) most be up-to-date with SDK tools like Hammer. Run the game once directly from the Steam window before running Hammer and compiling the map. Make sure Steam has fully downloaded all the game files (download reaches 100%). Running the games will ensure that the game and Hammer are using the same version of essential engine files.
Run the map manually
- If you are using the normal compile mode, check the Don't run the game after compiling option. If you are using expert compile mode, make sure that Hammer is not launching the game after the map is compiled.
- After the compile process has finished, manually launch the game from Steam.
- After the game has launched, click the "Create Server" option from the game menu, and play your map from there.