I've installed InstallShield LE for Visual Studio 2012 and created an msi. It works fine installing on a 64 bit machine, but on a 32 bit machine I get an error "(null) is not a valid Win32 application".
My project is built to support Any CPU as the platform target.
If your machine is 64 bit, it will only make the 64 bit .msi file when you build "Any CPU". I had the same issue and found the best solution is just to use a 32 bit platform or make two separate projects and have two different installers. If you want to have both 32 bit and 64 bit .msi files in a single setup project you have to get the Pro version.
The answer to this question discuses how to do this. Installshield 2012 : Identify 32 or 64 bit Operating system and install appropriate ActiveX control - Basic msi installer