How do I resolve "Please make sure that the file is accessible and that it is a valid assembly or COM component"?

Question

I am building a project with OpenCV in C#. It requires a dll file called cvextern.dll. but, when adding this file as a reference, this message appears :-

a reference "cvextern.dll" can't be added, Please make sure that the file is accessible and that it is a valid assembly or COM component.

I get tired from searching, I spent the past 2 days in searching for a solution for that problem

Did you validated if the file is 'accessible' as in have all permissions (read/execute access) for specific user. Also if you downloaded if from internet you may need to 'unblock' it. — YetAnotherUser, Aug 16 '11 at 15:09
the file is a native DLL which means you can't add it to a .NET project via Add Reference... you can use via DllImport (see http://msdn.microsoft.com/en-us/library/system.runtime.interopservices.dllimportattribute.aspx) — Yahia, Aug 16 '11 at 15:11
Possible duplicate of [A reference to the dll could not be added](https://stackoverflow.com/questions/3456758/a-reference-to-the-dll-could-not-be-added) — STF, Jul 10 '17 at 05:57
The answer that is provided [here](https://stackoverflow.com/a/12639732/1017953) was the solution in my case. — Memet Olsen, Sep 28 '12 at 12:05

score 32 · Answer 1 · edited Oct 25 '18 at 14:45

32

In my case I had to register the .dll.

To do so, open cmd.exe (the console) with admin rights and type:

regsvr32 "foo.dll"

edited Oct 25 '18 at 14:45

Jesse Hufstetler

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answered Apr 05 '13 at 11:24

user2248818

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This is the answer probably 95% can of this error can be solved by doing this cmd -> `regsvr32 "C:\blah\foo.dll"` – SSpoke Jul 06 '15 at 03:42
This helps for me Thank you – Mansinh Mar 14 '18 at 12:34
4

I still get a similar error when I run this command. make sure the file is stored at the specified path etc – SeanMC Dec 06 '18 at 19:36

score 32 · Accepted Answer · answered Aug 16 '11 at 15:13

32

the file is a native DLL which means you can't add it to a .NET project via Add Reference... you can use it via DllImport (see http://msdn.microsoft.com/en-us/library/system.runtime.interopservices.dllimportattribute.aspx)

answered Aug 16 '11 at 15:13

Yahia

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the tutorial doesn't look like the reality .. Is the version of visual studio affects? I am using microsoft visual studio 2008 express edition .. :) – Omar Osama Aug 16 '11 at 15:30
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AFAIK is doesn't really matter... though the DLL must be either in the project directory or "globally accessible" (like system32...) – Yahia Aug 16 '11 at 15:39
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But how do you debug calls to that external dll if you can't add a reference to it in the project? – corporateAbaper Jun 19 '17 at 14:11
@DavidNogueira to debug the external DLL, you can attach your DLL-project (ie, the source & solution that built the DLL) to the process that loads the DLL at runtime. If the DLL being loaded and source match up, visual studio will let you step through the code – Soylent Graham Aug 27 '17 at 21:18
My program shows "An attempt was made to load a program with an incorrect format. (Exception from HRESULT: 0x8007000B)" error but by changing project build option from Any CPU to X86 solved my issue. [refer](https://stackoverflow.com/questions/2023766/an-attempt-was-made-to-load-a-program-with-an-incorrect-format-even-when-the-p/2024978#2024978) for more details. – Sushil Jadhav Dec 03 '18 at 09:15
Unfortunately what Yahia is saying is only *partially* true. **IFF you don't have the file in your project directory**, then you can't add it via Add Reference... Otherwise you should be fine. Just add it to the project directory. Don't do this ugly DllImport inside of code, that's hideous. – Yusha Feb 28 '19 at 17:48
this not working for me , when i wanna add the dll to the references is shows the error of the question and when i add it as you said the app exit with this code => has exited with code 255 (0xff). <= – makri aymen abderraouf Aug 01 '21 at 13:27

score 9 · Answer 3 · answered Aug 16 '11 at 15:27

9

Make sure the required dlls are exported (or copied manually) to the bin folder when building your application.

answered Aug 16 '11 at 15:27

billy

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Yes, since I could not add it as a reference but another DLL needed this. Simply copying at compile time worked. – Binarian Apr 14 '16 at 14:31

score 4 · Answer 4 · answered Dec 20 '17 at 23:40

'It' requires a dll file called cvextern.dll . 'It' can be either your own cs file or some other third party dll which you are using in your project.

To call native dlls to your own cs file, copy the dll into your project's root\lib directory and add it as an existing item. (Add -Existing item) and use Dllimport with correct location.

For third party , copy the native library to the folder where the third party library resides and add it as an existing item.

After building make sure that the required dlls are appearing in Build folder. In some cases it may not appear or get replaced in Build folder. Delete the Build folder manually and build again.

Some more details about "Add as existing item", once I copied the DLL to my bin/debug directory, in VS code I went to Project > add existing item> myLibrary.dll -it worked. Thanks for the tip! -See this: https://learn.microsoft.com/en-us/sql/ssms/solution/add-existing-items-to-a-project?view=sql-server-2017 — SeanMC, Dec 06 '18 at 19:52

score 3 · Answer 5 · answered Jul 07 '14 at 06:42

I had the same program, I hope this could help.

I your using Windows 7, open Command Prompt-> run as Administrator. register your <...>.dll.

Why run as Administrator, you can register your <...>.dll using the run at the Windows Start, but still your dll only run as user even your account is administrator.

Now you can add your <...>.dll at the Project->Add Reference->Browse

Thanks

gneri · Answer 6 · 2018-04-12T02:13:12.750

Look here for the answer by TheMattster. I implemented it and it worked like a charm. In a nutshell, his solution suggests to add the COM dll as a resource to the project (so now it compiles into the project's dll), and upon the first run write it to a file (i.e. the dll file I wanted there in the first place).

The following is taken from his answer.

Step 1) Add the DLL as a resource (below as "Resources.DllFile"). To do this open project properties, select the resources tab, select "add existing file" and add the DLL as a resource.

Step 2) Add the name of the DLL as a string resource (below as "Resources.DllName").

Step 3) Add this code to your main form-load:

if (!File.Exists(Properties.Resources.DllName))
{
    var outStream = new StreamWriter(Properties.Resources.DllName, false);
    var binStream = new BinaryWriter(outStream.BaseStream);
    binStream.Write(Properties.Resources.DllFile);
    binStream.Close();
}

My problem was that not only I had to use the COM dll in my project, I also had to deploy it with my app using ClickOnce, and without being able to add reference to it in my project the above solution is practically the only one that worked.

If possible you ought to copy the relevant details into your answer. — StayOnTarget, Apr 11 '18 at 19:22
I don't know if possible, but I understand we should have it here in case the link stops functioning. — gneri, Apr 12 '18 at 02:14

score 1 · Answer 7 · edited Apr 07 '20 at 11:03

In my case I also have unmanaged dll's (C++) in workspace and if you specify:

<files>
    <file src="bin\*.dll" target="lib" />
</files>

nuget would try to load every dll as an assembly, even the C++ libraries! To avoid this behaviour explicitly define your C# assemblies with references tag:

<references>
    <reference file="Managed1.dll" />
    <reference file="Managed2.dll" />
</references>

Remark: parent of references is metadata -> according to documentation https://learn.microsoft.com/en-us/nuget/reference/nuspec#general-form-and-schema

Documentation: https://learn.microsoft.com/en-us/nuget/reference/nuspec

How do I resolve "Please make sure that the file is accessible and that it is a valid assembly or COM component"?

7 Answers7

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