Not a valid Win32 application' error

Those of us who spend our working lives developing Windows applications will have seen it a million times. End users will also be familiar with this error. Anyone who spent time in the 1990s downloading files over dial-up connections (which could easily be disconnected) will also get a shudder of recognition at this message. That bleep of a Windows error, that reassuredly vague dialogue box, the knowledge that you are  now pretty much stumped. But what exactly does ‘Not a valid Win32 application’ error mean? And why does it occur?

What does it mean?
In short this error is describing a corrupted Windows .exe file. Why exactly this occurs, we shall look at shortly. This error typically occurs when an executable file is either incomplete, or has been only partially downloaded from the web. Developers will see this error when creating and running apps in their chosen IDE, often when there has been a DLL or compile error.

Why does it occur?
There are a large number of reasons for this error, and herein lies the crux of the problem. ‘Not a valid Win32 application’ is basically a bit of a catch all, a grouping together of problems that all suffer from the same thing - file corruption. We are able to break down the causes a little:

1. File corruption: This is typically the root cause. File corruption can occur when a file hasn’t downloaded correctly, or as a result of a  corrupted hard disk.
2. File extension: Executable files have the 3 letter extension ‘.exe’. Occasionally this extension can be changed (due to user error or misconfiguration) and can result in the Win32 error.
3. Malware or Virus: Various forms of virus and malware software can cause this error, by either corrupting the executable file in question, or some other part of the filesystem.
4. Wrong operating system: This error can also occur if a 32bit Windows application tries to run on a 64bit Windows environment. Similarly it can happen if a modern application is ran on a much older version of Windows, like XP.

Developers will often see this error when compiling their applications and running the executable on a different platform, or running the file without the correct DLL (Dynamic Linked library, containing shared libraries) files present

Possible fixes
For many, simply re-downloading the file in question will fix the problem. More serious causes (corrupted disk drives or a virus) will require a bit more work. Running a trusted malware or virus scanner, and checking the integrity of the hard disk, are the best bets.

Addressing this error in a development environment is a bit more complex, as it very much depends how the application is being compiled. As every developer will know, debugging errors can be tricky for even the simplest thing. So where do you start? Here are a few things to try:

1. Be clear in Visual Studio if you are compiling for 64-bit or 32-bit environments. Often it is best to target ‘Any CPU’.
2. If you are creating a Windows XP app, be sure to set the ‘Platform Toolset’ to ‘Windows XP (V110_xp)’. Anyone using Visual Studio 2012 will need Update 1 to target older Windows platforms.
3. Check what version of .NET your application is using. Later versions (4.5) don’t support Windows XP or Windows Server 2003

Good luck