c# - using LoadLibrary returns 0 with Win32Error 193

I'm building a c# class library that calls third party DLLs supplied by a vendor we're working with. The vendors examples are all in vc++ and are running and working.

I'm trying to load one of the DLLs and it's returning an IntPtr 0. When I call Marshal.GetLastWin32Error() I get 193 which from what I've read means that I'm trying to load a 32-bit DLL in 64-bit app. But I checked again and again and both my class library is set to x86 and my console application that makes the call to that class library is set to x86.

I can successfully load other DLL files by the same vendor (which are also 32-bit).

This is my Native helper class:

class NativeHelper
{
    [DllImport("kernel32.dll", EntryPoint = "LoadLibrary", SetLastError = true)]
    public static extern IntPtr LoadLibrary(string dllToLoad);

    [DllImport("kernel32.dll", EntryPoint = "LoadLibraryEx", SetLastError = true)]
    public static extern IntPtr LoadLibraryEx(string dllToLoad, IntPtr hFile, LoadLibraryFlags flags);

    [DllImport("kernel32.dll")]
    public static extern IntPtr GetProcAddress(IntPtr hModule, string procedureName);

    [DllImport("kernel32.dll")]
    public static extern bool FreeLibrary(IntPtr hModule);

    [System.Flags]
    public enum LoadLibraryFlags : uint
    {
        DONT_RESOLVE_DLL_REFERENCES = 0x00000001,
        LOAD_IGNORE_CODE_AUTHZ_LEVEL = 0x00000010,
        LOAD_LIBRARY_AS_DATAFILE = 0x00000002,
        LOAD_LIBRARY_AS_DATAFILE_EXCLUSIVE = 0x00000040,
        LOAD_LIBRARY_AS_IMAGE_RESOURCE = 0x00000020,
        LOAD_WITH_ALTERED_SEARCH_PATH = 0x00000008,
        LOAD_LIBRARY_SEARCH_DLL_LOAD_DIR = 0x00000100,
        LOAD_LIBRARY_SEARCH_SYSTEM32 = 0x00000800,
        LOAD_LIBRARY_SEARCH_DEFAULT_DIRS = 0x00001000
    }
}

And this is how I make the call:

IntPtr pDll = NativeHelper.LoadLibrary(@"dhplay.dll"); // returns 0
if (pDll == IntPtr.Zero)
{
    var err = Marshal.GetLastWin32Error().ToString(); // returns 193
    Console.WriteLine(err);
}

What am I missing here? If I'm running x86 why is that DLL not loaded and others do?

Edit (Additional information):

IntPtr.Size is 4

dumpbin returns 8664 machine (x64) - That means it's 64-bit? I checked for other DLL used and they are 8664 machine (x86)

As far as dependencies, it's working on a vc++ application on my machine.

If there is smoke, there is often fire. Some dll is probably x64 while your app is x32 (or the reverse).

• Check in you app IntPtr.Size. 4 → x86, 32 bits, 8 → x64, 64 bits

• If you use the Visual Studio Command Prompt, you should be able to use dumpbin. Do a dumpbin /headers yourdll.dll | more for your dlls. One of the first rows should be machine (...). In the (...) it should be written if it is x86 (so 32 bits) or x64 (so 64 bits)

To the second question, you can't in any way mix 32 and 64 bit dlls in a single process. Some programs "cheat" and create a secondary process with the correct bits to load the dlls and then do IPC (inter-process-communication) between the primary process and the secondary process to use the dll. Clearly it is complex.