SetupArrayProps R: array prop 'null' is at index zero

The startup error SetupArrayProps R: array prop 'null' is at index zero is caused by trying to run a Source 2007 game/mod with the Source 2009 engine. This is not possible.

Solution

The only Source 2007 game left today is Source SDK Base 2007. To use it:

• Change the SteamAppId value in gameinfo.txt file to 218, then restart Steam.
• Make any sure that any paths to hl2.exe (such as the launch path for the Visual Studio debugger) are pointing to SteamApps/account_name/source sdk base 2007/hl2.exe.

To access content from a 2009 game while still using the 2007 engine, see mounting multiple games.