Failed to load the launcher DLL: %1 is not a valid Win32 application.

[JuneCoreEngine]

Same as title, I put hl2_launcher.exe in my hl2 game install folder, and also tried this:

[AFellowSpeedrunner]

You need to copy the bin/ folder to the root of your install and the hl2/bin folder to your install folder too.

for example:

source/hl2/bin -> Half-Life 2/bin

source/hl2/hl2/bin Half-Life 2/hl2/bin

Make sure you are also launching hl2_launcher.exe and not your hl2.exe. They will not work mixed due to code differences between the two.

Hope this helps!