Your DirectX Runtime is out of date

For some people Garry's Mod will show this error on start up:

Your DirectX Runtime is out of date.
Download and install this file from Microsoft.

This start up crash is caused by Garry's Mod not being able to load this file in your system:

• C:/Windows/System32/D3DX9_40.dll

or for 64bit systems:

• C:/Windows/SysWOW64/D3DX9_40.dll

Which is a part of DirectX 9.0c Runtime Libraries, necessary to run the game.

To fix this problem you simply have to install/update your DirectX 9.0c Runtime Libraries.

Please make sure to allow Steam to install this software on first launch of Garry's Mod by pressing "Yes" and allow "Steam Client Service" to make changes to your PC if prompted when you start the game through Steam. 

If that does not happen or help, please follow the following steps:

• Please navigate to the Steam folder on your computer, by default this is:
  • C:\Program Files (x86)\Steam\
  • The location may be different on your computer if you changed it during Steam installation
• In the Steam folder navigate to:
  • SteamApps\common\Steamworks Shared\_CommonRedist\DirectX\Jun2010
• Run the DXSETUP.EXE file and complete the installation process.

If that does not help, please follow the following steps:

• Please navigate to the following folder:
  
  • C:\Windows\SysWOW64
• And delete or rename the file named "D3DX9_40.dll". (You may need administrator privileges to do so)
• Then try to complete the DXSETUP.EXE installation again.

If that does not help still, please follow the following steps:

• Please navigate to this folder:
  • C:\Windows\System32
• And delete or rename the file named "D3DX9_40.dll". (You may need administrator privileges to do so)
• Then try to complete the DXSETUP.EXE installation again.

This should solve your problem.