GTA IV won't start: 'SecuLauncer failed to start application' error?
Solution 1:
From SecuROM's website:
Please note that this is a common issue when the Visual Studio C++ redistributable and/or Microsoft .NET Framework 3.5 was not installed properly.
To solve the issue, please open your Windows Explorer/My Computer and switch to the following directory on the 'Grand Theft Auto IV' Disc #1: e.g. E:\GTAIV\Redistributable.
If you own the Steam download version, please open your installation path of 'Grand Theft Auto IV': e.g. C:/Progra...steamapps/common/grand theft auto iv/installers.
In that folder you will find a file called 'vcredist_x86.exe'. Please execute this application and follow the installation wizard.
Please also download and install the latest version of Microsoft .NET Framework 3.5.
After you have successfully installed the Visual Studio C++ redistributable and Microsoft .NET Framework 3.5 please perform the recommended reboot. 'Grand Theft Auto IV' should start fine now.
Technically, this is something that Steam should have handled when you first ran it. But ensuring you have the correct dependencies installed should do the trick.