Unable to load DLL Module could not be found HRESULT 0x8007007E

Question

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

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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

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

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Try to enter the full-path of the dll  If it doesn t work  try to copy the dll into the system32 folder

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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

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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

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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

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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

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From what I remember on Windows the search order for a dll is    Current Directory System folder  C  windows system32 or c  windows SysWOW64  for 32-bit process on 64-bit box   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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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

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