Unable to launch onscreen keyboard (osk.exe) from a 32-bit process on Win7 x64

I don't have a very solid explanation for the exact error message you are getting. But disabling redirection is going to mess up the .NET framework. By default, Process.Start() P/Invokes the ShellExecuteEx() API function to start the process. This function lives in shell32.dll, a DLL that might have to be loaded if that wasn't previously done. You'll get the wrong one when you disable redirection.

A workaround for that is to set ProcessStartInfo.UseShellExecute to false. You don't need it here.

Clearly, disabling redirection is a risky approach with side-effects you cannot really predict. There are lots of DLLs that get demand-loaded. A very small helper EXE that you compile with Platform Target = Any CPU can solve your problem.

A 32 bit application running on a 64 bit operating system should start the 64 bit version of osk.exe. Below you see a code snipped written in C# to start the correct on screen keyboard.

    private static void ShowKeyboard()
    {
        var path64 = @"C:\Windows\winsxs\amd64_microsoft-windows-osk_31bf3856ad364e35_6.1.7600.16385_none_06b1c513739fb828\osk.exe";
        var path32 = @"C:\windows\system32\osk.exe";
        var path = (Environment.Is64BitOperatingSystem) ? path64 : path32;
        Process.Start(path);
    }