[c#] Unable to load DLL (Module could not be found HRESULT: 0x8007007E)

I have dll library with unmanaged C++ API code I need to use in my .NET 4.0 application. But every method i try to load my dll i get an error:

Unable to load DLL 'MyOwn.dll': The specified module could not be found. (Exception from HRESULT: 0x8007007E)

I have read and tried severa solutions i have found on the internet. Nothing works..

I have tried using following methods:

[DllImport("MyOwn.dll",  CallingConvention = CallingConvention.Cdecl)]
[return: MarshalAs((UnmanagedType.I4))]
public static extern Int32 MyProIni(string DBname, string DBuser_pass,
    string WorkDirectory, ref StringBuilder ErrorMessage);

When I tried following this article and when I run this example (from the downloaded code) it runs without a problem (the dll used is in the bin/debug folder)

I have copied my dll (along with all files the it depends on into my bin folder).

I also tried this approach but got the same error:

[DllImportAttribute(MyOwnLibDllPath, EntryPoint="TMproIni")]
[return: MarshalAs(UnmanagedType.I4)]
public static extern  int MyproIni(string DBname, string DBuser_pass, 
    string WorkDirectory, ref StringBuilder ErrorMessage);

Any suggestions?

The DLL has to be in the bin folder.

In Visual Studio, I add the dll to my project (NOT in References, but "Add existing file"). Then set the "Copy to Output Directory" Property for the dll to "Copy if newer".

Also faced the same problem when using unmanaged c/c++ dll file in c# environment.

1.Checked the compatibility of dll with 32bit or 64bit CPU.

2.Checked the correct paths of DLL .bin folder, system32/sysWOW64 , or given path.

3.Checked if PDB(Programme Database) files are missing.This video gives you ans best undestand about pdb files.

When running 32-bit C/C++ binary code in 64bit system, could arise this because of platform incompatibility. You can change it from Build>Configuration manager.

Make sure you set the Build Platform Target to x86 or x64 so that it is compatible with your DLL - which might be compiled for a 32 bit platform.

There is one very funny thing (and has a technical relevance) which might waste your hours so thought of sharing it here -

I created a console application project ConsoleApplication1 and a class library project ClassLibrary1.

All the code which was making the p/invoke was present in ClassLibrary1.dll. So before debugging the application from visual studio I simply copied the C++ unmanaged assembly (myUnmanagedFunctions.dll) into the \bin\debug\ directory of ClassLibrary1 project so that it can be loaded at run-time by the CLR.

I kept getting the

Unable to load DLL

error for hours. Later on I realized that all such unmanaged assemblies which are to be loaded need to be copied into the \bin\debug directory of the start-up project ConsoleApplication1 which is usually a win form, console or web application.

So please be cautious the Current Directory in the accepted answer actually means Current Directory of main executable from where you application process is starting. Looks like an obvious thing but might not be so at times.

Lesson Learnt - Always place the unamanaged dlls in the same directory as the start-up executable to ensure that it can be found.

You can use the dumpbin tool to find out the required DLL dependencies:

dumpbin /DEPENDENTS my.dll

This will tell you which DLLs your DLL needs to load. Particularly look out for MSVCR*.dll. I have seen your error code occur when the correct Visual C++ Redistributable is not installed.

You can get the "Visual C++ Redistributable Packages for Visual Studio 2013" from the Microsoft website. It installs c:\windows\system32\MSVCR120.dll

In the file name, 120 = 12.0 = Visual Studio 2013.

Be careful that you have the right Visual Studio version (10.0 = VS 10, 11 = VS 2012, 12.0 = VS 2013...) right architecture (x64 or x86) for your DLL's target platform, and also you need to be careful around debug builds. The debug build of a DLL depends on MSVCR120d.dll which is a debug version of the library, which is installed with Visual Studio but not by the Redistributable Package.

This is a 'kludge' but you could at least use it to sanity-test: Try hard-coding the path to the DLL in your code

[DllImport(@"C:\\mycompany\\MyDLL.dll")]

Having said that; in my case running dumpbin /DEPENDENTS as suggested by @anthony-hayward, and copying over 32-bit versions of the DLLs listed there into my working directory solved this problem for me.

The message is just a bit misleading, becuase it isn't "my" dll that can't be loaded - it's the dependencies

Turn on the fusion logging, see this question for lots of advice on how to do that. Debugging mixed-mode apps loading problems can be a right royal pain. The fusion logging can be a big help.

I had the same problem when I deployed my application to test PC. The problem was development PC had msvcp110d.dll and msvcr110d.dll but not the test PC.

I added "Visual Studio C++ 11.0 DebugCRT (x86)" merge module in InstalledSheild and it worked. Hope this will be helpful for someone else.

Setup: 32-bit Windows 7

Context: Installed a PCI-GPIB driver that I was unable to communicate through due to the aforementioned issue.

Short Answer: Reinstall the driver.

Long Answer: I also used Dependency Walker, which identified several missing dependency modules. Immediately, I thought that it must have been a botched driver installation. I didn't want to check and restore each missing file.

The fact that I was unable to find the uninstaller under Programs and Features of the Control Panel is another indicator of bad installation. I had to manually delete a couple of *.dll in \system32 and registry keys to allow for driver re-installation.

Issue fixed.

The unexpected part was that not all dependency modules were resolved. Nevertheless, the *.dll of interest can now be referenced.

From what I remember on Windows the search order for a dll is:

1. Current Directory
2. System folder, C:\windows\system32 or c:\windows\SysWOW64 (for 32-bit process on 64-bit box).
3. Reading from the Path environment variable

In addition I'd check the dependencies of the DLL, the dependency walker provided with Visual Studio can help you out here, it can also be downloaded for free: http://www.dependencywalker.com

I have come across the same problem, In my case I had two 32 bit pcs. One with .NET4.5 installed and other one was fresh PC.

my 32-bit cpp dll(Release mode build) was working fine with .NET installed PC but Not with fresh PC where I got the below error

Unable to load DLL 'PrinterSettings.dll': The specified module could not be found. (Exception from HRESULT: 0x8007007E)

finally,

I just built my project in Debug mode configuration and this time my cpp dll was working fine.

If the DLL and the .NET projects are in the same solution and you want to compile and run both every time, you can right click the properties of the .NET project, Build events, then add something like the following to Post-build event command line:

copy $(SolutionDir)Debug\MyOwn.dll .

It's basically a DOS line, and you can tweak based on where your DLL is being built to.

Ensure that all dependencies of your own dll are present near the dll, or in System32.

I faced the same problem when import C++ Dll in .Net Framework +4, I unchecked Project->Properties->Build->Prefer 32-bit and it solved for me.

Try to enter the full-path of the dll. If it doesn't work, try to copy the dll into the system32 folder.

I think your unmanaged library needs a manifest.
Here is how to add it to your binary. and here is why.

In summary, several Redistributable library versions can be installed in your box but only one of them should satisfy your App, and it might not be the default, so you need to tell the system the version your library needs, that's why the manifest.

In my case one unmanaged dll was depending on another which was missing. In that case the error will point to the existing dll instead of the missing one which can be really confusing.

That is exactly what had happen in my case. Hope this helps someone else.