A reference to the dll could not be added

Question

When I add a  dll file as a reference in C  application it shows an error       A reference to the      dll  could not be added Please make sure that   the file is accessible and that it is a valid assembly or COM   component    ILDissassembler says there is no valid CLR header so I try to register it using regsvr32 and that gives me another error       The module    was loaded but the call to DLLRegisterServer failed with   error code  0x80004005    I am using VS2010 ultimate version on a 64bit Windows 7 machine  What could be the problem   Thanks for any hints replies

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I needed to change architecture to x86 from x64 in configuration manager and copy my 32 bit dll (C language - pcProxAPI.dll) into new folder this created.. This is on top of the steps described by "Sashus" below.

C:\Projects..\bin\x86\Debug

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I had this issue after my PC has been restarted during building the solution  My two references gone  so I had to rebuild my two projects manually and then I could add references without error

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Make sure your compiler is set to x86 if you are trying to reference an x86 dll     I was having similar issues    as mentioned above  trying to use OLEDB to access an Excel file from my C  code in Visual Studio 2012   I kept getting errors about the Access library not being accessible but I knew that I had loaded it   During Debug  it dawned on me that I am compiling for 64 bit but have Office x86 loaded  Even though I loaded the Access library for 32 bit  it was never being used by the app    and was  therefore  not accessible   Here is what I was using in C     Provider Microsoft ACE OLEDB 12 0 Data Source     strFilePath     Extended Properties  Excel 12 0 Xml HDR Yes         I  was getting an error  As soon as I switched the compiler to x86 it worked

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For anyone else looking for help on this matter  or experiencing a FileNotFoundException or a FirstChanceException  check out my answer here    A first chance exception of type   39 System IO FileNotFoundException  39  occurred in mscorlib ni dll - windows phone  In general you must be absolutely certain that you are meeting all of the requirements for making the reference - I know it s the obvious answer  but you re probably overlooking a relatively simple requirement

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I just ran into that issue and after all the explanations about fixing it with command prompt I found that if you add it directly to the project you can  then simply include the library on each page that it s needed

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You can add a DLL  or EXE  to a project only if it is a  NET assembly  If it s not you will see this error message   regsvr32 also makes certain assumptions about the structure and exported function in the DLL  It has been a while since I used it but it has to do with registering COM servers so certain entry points need to be available  If regsvr32 fails the DLL doesn t provide those entry points and the DLL does not contain a COM component   You only chance for using the DLL is to import it like any other non- NET binary  e g  when you use certain Win32 APIs  There is an old MSDN Magazine Article that might be helpful  See the following update for info where to get the article   Update 12 March 2018  The link to the MSDN Magazine no longer works as it used to in August 2010  The article by Jason Clark is titled   NET Column  Calling Win32 DLLs in C  with P Invoke   It was published in the July 2010 issue of MSDN Magazine  The  Wayback Machine  has the article here at the moment  formatting is limited   The entire MSDN Magazine issue July 2010 is available here  HCM format only  instructions for how to use HCM files here

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Normally in Visual Studio 2015 you should create the dll project as a C   -  CLR project from Visual Studio s templates  but you can technically enable it after the fact   The critical property is called Common Language Runtime Support set in your project s configuration  It s found under Configuration Properties  gt  General  gt  Common Language Runtime Support   When doing this  VS will probably not update the  Target  NET Framework  option  like it should   You can manually add this by unloading your project  editing the your project xxproj file  and adding updating the Target  NET framework Version XML tag   For a sample  I suggest creating a new solution as a C   CLR project and examining the XML there  perhaps even diffing it to make sure there s nothing very important that s out of the ordinary

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You can not add a reference to a native DLL  However You can include them in the solution  right click solution  select  Add existing file    but they will not be referenced unless you declare something like   DllImport         public static extern void MyFunction      Maybe there s some kind of wrapper DLL  which you are actually referencing and which contains the DLL imports   Sometimes  You may reference the wrapper DLL but still can not make your program running  where error prompt suggests you to ensure the file exists and all dependencies are available    This problem is because the assembly you are trying to add is targeted and compiled only for a x86 or x64 processor architecture    Just try change the Target Platform to x86 or x64 in Build -  Configuration Manager

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start cmd exe and type  Regsvr32  dllpath    dllpath   replace to your dll path

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I had this error while writing a Windows Service  I was running Visual Studio as Administrator so that my post build commands would automatically install my service  I noticed that when I closed everything and ran VS normally  Not as Administrator  it let me add the references just fine with no error   Hope this solution works for you

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My answer is a bit late  but as a quick test  make sure you are using the latest version of libraries    In my case after updating a nuget library that was referencing another library causing the problem the problem disappeared

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I had the same problem when I tried to add a dll I just coded in C   to my new C  project  Turned out I needed to set properties of the C   project my dll is from    Configuration Properties General Common Language Runtime Support   clr Configuration Properties C C   General Common Language RunTime Support   clr   Because the C  project in which I wanted to use this dll was also set like that  had the same properties set to  clr

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I used dependency walker to check out the internal references the dll was having  Turns out it was in need of the VB runtime msvbvm60 dll and since my dev box doesnt have that installed I was unable to register it using regsvr32  That seems to be the answer to my original question for now

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You can add  dll file manually  For example if you want to add a dll file in your WPF application  and you are unable to refer it in your project   Getting error  A reference to the      dll  could not be added Please make sure that the file is accessible and that it is a valid assembly or COM component     then COPY that dll file and PASTE in the  INSTALLER PROJECT  in application folder

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I have the same problem with importing WinSCard dll in my project  I deal with that importing directly from dll like this    DllImport  winscard dll    public static extern int SCardEstablishContext int dwScope  int pvReserved1  int pvReserved2  ref int phContext     DllImport  winscard dll    public static extern int SCardReleaseContext int phContext     You could add this to separate project and then add a reference from your main project

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I faced a similar problem   I was trying to add the reference of a  net 2 0 dll   to a  Net 1 1 project  When I tried adding a previous version of the  dll which was complied in  Net 1 1  it worked for me

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The following worked for me   Short answer  Run the following via command line  cmd    TlbImp exe cvextern dll          where cvextern dll is your dll you want to fix    And a valid dll will be created for you   Longer answer   Open cmd Find TlbImp exe  Probably located in C  Program Files  x86  Microsoft SDKs Windows v7 0A Bin  If you can t find it go to your root folder  C   or D   and run   dir tlbimp exe  s                this will locate the file   Run tlbimp exe and put your dll behind it  Example  If your dll is cvextern dll  You can run   TlbImp exe cvextern dll  A new dll has been created in the same folder of tlbimp exe  You can use that as reference in your project

[.net] A reference to the dll could not be added

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